.7 


Qi^^\A- 


VTS^ 


Columbia  ^ttiber^ittp  ^f 

(Dnll^g^  of  pijgHtrtattH  nnh  ^ttrgrnna 


i^partm^nt  nf  pli^Btologg 


The 
Organism  as  a  Whole 

From   a   Physicochemical  Viewpoint 


By 

Jacques  Loeb,  m.d.,  Ph.D.,  Sc.D. 

Member  of  the  Rockefeller  Institute  for  Medical  Research 


With  51  Illustrations 


G.  P.  Putnam»s  Sons 

New  York  and  London 

^bc  IRntcfterbocf^ec  press 

1916 


Copyright,  1916 

BY 

JACQUES  LOEB 


Ttbe  ftnfclicrbocktt  press,  -new  l|?ort 


XTo 

THE   MEMORY   OF 

DENIS   DIDEROT 

Of  the  Encydopedie  and  the  Systeme  de  la  nature 


"  He  was  one  of  those  simple,  disinterested, 
and  intellectually  sterling  workers  to 
whom  their  own  personality  is  as  nothing 
in  the  presence  of  the  vast  subjects  that 
engage  the  thoughts  of  their  lives." 

John  Morley. 

(Article  Diderot,  EncyclopcBdia  Britannica.) 


Digitized  by  tine  Internet  Arciiive 

in  2010  witii  funding  from 

Open  Knowledge  Commons  (for  the  Medical  Heritage  Library  project) 


http://www.archive.org/details/organismaswholOOIoeb 


PREFACE 

It  is  generally  admitted  that  the  individual  physio- 
logical processes,  such  as  digestion,  metabolism,  the 
production  of  heat  or  of  electricity,  are  of  a  purely 
physicochemical  character;  and  it  is  also  conceded  that 
the  fimctions  of  individual  organs,  such  as  the  eye  or 
the  ear,  are  to  be  analysed  from  the  viewpoint  of  the 
physicist.  When,  however,  the  biologist  is  confronted 
with  the  fact  that  in  the  organism  the  parts  are  so 
adapted  to  each  other  as  to  give  rise  to  a  harmonious 
whole;  and  that  the  organisms  are  endowed  with 
structures  and  instincts  calculated  to  prolong  their  life 
and  perpetuate  their  race,  doubts  as  to  the  adequacy  of 
a  purely  physicochemical  viewpoint  in  biology  may 
arise.  The  difficulties  besetting  the  biologist  in  this 
problem  have  been  rather  increased  than  diminished 
by  the  discovery  of  Mendelian  heredity,  according  to 
which  each  character  is  transmitted  independently  of 
any  other  character.  Since  the  number  of  MendeHan 
characters  in  each  organism  is  large,  the  possibility 
must  be  faced  that  the  organism  ismerely  a  mosaic  of 
independent  hereditary  characters.    If  this  be  the  case 


vi  Preface 

the  question  arises:  What  moulds  these  independent 
characters  into  a  harmonious  whole? 

The  vitahst  settles  this  question  by  assuming  the 
existence  of  a  pre-established  design  for  each  organism 
and  of  a  guiding  "force"  or  "principle"  which  directs 
the  working  out  of  this  design.  Such  assumptions 
remove  the  problem  of  accounting  for  the  harmonious 
character  of  the  organism  from  the  field  of  physics  or 
chemistry.  The  theory  of  natural  selection  invokes 
neither  design  nor  purpose,  but  it  is  incomplete  since 
it  disregards  the  physicochemical  constitution  of  living 
matter  about  which  little  was  known  until  recently. 

In  this  book  an  attempt  is  made  to  show  that  the 
unity  of  the  organism  is  due  to  the  fact  that  the  egg 
(or  rather  its  cytoplasm)  is  the  future  embryo  upon 
which  the  Mendelian  factors  in  the  chromosomes  can 
impress  only  individual  characteristics,  probably  by 
giving  rise  to  special  hormones  and  enzymes.  We  can 
cause  an  egg  to  develop  into  an  organism  without  a 
spermatozoon,  but  apparently  we  cannot  make  a  sperm- 
atozoon develop  into  an  organism  without  the  cyto- 
plasm of  an  egg,  although  sperm  and  egg  nucleus 
transmit  equally  the  Mendelian  characters.  The  con- 
ception that  the  cytoplasm  of  the  egg  is  already  the 
embryo  in  the  rough  may  be  of  importance  also  for  the 
problem  of  evolution  since  it  suggests  the  possibility 
that  the  genus-  and  species-heredity  are  determined  by 
the  cytoplasm  of  the  egg,  while  the  Mendelian  heredi- 


Preface  vii 

tary  characters  cannot  contribute  at  all  or  only  to  a 
Lknited  extent  to  the  formation  of  new  species.  Such 
an  idea  is  supported  by  the  work  on  immunity,  which 
shows  that  genus-  and  probably  species-specificity  are 
due  to  specific  proteias,  while  the  Mendelian  characters 
may  be  determined  by  hormones  which  need  neither  be 
proteins  nor  specific  or  by  enzymes  which  also  need 
not  be  specific  for  the  species  or  genus.  Such  a  con- 
ception would  remove  the  difficulties  which  the  work  on 
Mendelian  heredity  has  seemingly  created  not  only  for 
the  problem  of  evolution  but  also  for  the  problem  of 
the  harmonious  character  of  the  organism  as  a  whole. 

Since  the  book  is  intended  as  a  companion  volume 
to  the  writer's  former  treatise  on  The  Comparative 
Physiology  of  the  Brain  a  discussion  of  the  functions  of 
the  central  nervous  system  is  omitted. 

Completeness  in  regard  to  quotation  of  literature 
was  out  of  the  question,  but  the  writer  notices  with 
regret,  that  he  has  failed  to  refer  in  the  text  to  so 
important  a  contribution  to  the  subject  as  Sir  E.  A. 
Schafer's  masterly  presidential  address  on  "Life  "  or 
the  addresses  of  Correns  and  Goldschmidt  on  the  de- 
termination of  sex.  Credit  should  also  have  been  given 
to  Professor  Raymond  Pearl  for  the  discrimination  be- 
tween species  and  individual  inheritance. 

The  writer  wishes  to  acknowledge  his  indebtedness 
to  his  friends  Professor  E.  G.  Conklin  of  Princeton, 
Professor  Richard  Goldschmidt  of  the  Kaiser  Wilhelm 


Vlll 


Preface 


Institut  of  Berlin,  Dr.  P.  A,  Levene  of  the  Rockefeller 
Institute,  Professor  T.  H.  Morgan  of  Columbia  Univer- 
sity, and  Professor  Hardolph  Wasteneys  of  the  Univer- 
sity of  California  who  kindly  read  one  or  more  chapters 
of  the  book  and  offered  valuable  suggestions;  and  he 
wishes  especially  to  thank  his  wife  for  suggesting  many 
corrections  in  the  manuscript  and  the  proof. 

The  book  is  dedicated  to  that  group  of  freethinkers, 
including  d'Alembert,  Diderot,  Holbach,  and  Voltaire, 
who  first  dared  to  follow  the  consequences  of  a  mechan- 
istic science — incomplete  as  it  then  was — to  the  rules  of 
human  conduct  and  who  thereby  laid  the  foundation  of 
that  spirit  of  tolerance,  justice,  and  gentleness  which 
was  the  hope  of  our  civilization  until  it  was  buried 
under  the  wave  of  homicidal  emotion  which  has  swept 
through  the  world.  Diderot  was  singled  out,  since  to 
him  the  words  of  Lord  Morley  are  devoted,  which, 
however,  are  more  or  less  characteristic  of  the  whole 
group. 


J.  L. 


The  Rockefeller  Institute 

FOR  Medical  Research, 

August,  1 916 


CONTENTS 

CHAPTER  I 

FAGB 

Introductory  Remarks i 

CHAPTER  II 

The  Specific  Difference  between  Living  and 
Dead  Matter  and  the  Question  of  the 
Origin  of  Life     ......       14 

CHAPTER  III 

The   Chemical   Basis   of    Genus    and    Species:      40 
L — The     Incompatibility     of    Species     not 

Closely  Related  .....       44 
II. — The  Chemical  Basis  of  Genus  and  Species 

AND  of  Species  Specificity    ...      53 

CHAPTER  IV 
Specificity  in  Fertilization       .         .        .      ".      71 

CHAPTER  V, 
Artificial  Parthenogenesis        .         .        .        .      95 

CHAPTER  VI 

Determinism  in  the  Formation  of  an  Organism 

FROM  AN  Egg 128 

ix 


X  Contents 

CHAPTER  VII 

PAGE 

Regeneration i53 

CHAPTER  VIII 

Determination     of     Sex,     Secondary     Sexual 
Characters,  and  Sexual  Instincts: 
I. — The    Cytological   Basis  of    Sex    Deter- 
mination        .         .         .         .         .         .198 

II. — The    Physiological    Basis    of    Sex    De- 
termination ,         .         .         .         .         .214 

CHAPTER  IX 

Mendelian  Heredity  and  its  Mechanism  .         .     229 

CHAPTER  X 

Animal  Instincts  and  Tropisms  .         .         .253 

CHAPTER  XI 

The  Influence  of  Environment    .    .    .  286 

CHAPTER  XII 

Adaptation  to  Environment       ,         .         .         •     31^ 

CHAPTER  XIII 

Evolution 34^ 

CHAPTER  XIV 

Death  and  Dissolution  of  the  Organism           .      349 
Index 37i 


The  Organism  as  a  Whole 


a7,(\f'(!:\(.rinVf. 


The  Organism  as  a  Whole 


CHAPTER  I 

INTRODUCTORY  REMARKS 

I.  The  physical  researches  of  the  last  ten  years  have 
put  the  atomistic  theory  of  matter  and  electricity  on 
a  definite  and  in  all  probability  permanent  basis.  We 
know  the  exact  number  of  molecules  in  a  given  mass 
of  any  substance  whose  molecular  weight  is  known  to 
us,  and  we  know  the  exact  charge  of  a  single  electron. 
This  permits  us  to  state  as  the  ultimate  aim  of  the 
physical  sciences  the  visualization  of  all  phenomena 
in  terms  of  groupings  and  displacements  of  ultimate 
particles,  and  since  there  is  no  discontinuity  between 
the  matter  constituting  the  living  and  non-living  world 
the  goal  of  biology  can  be  expressed  in  the  same  way. 

This  idea  has  more  or  less  consciously  prevailed  for 
some  time  in  the  explanation  of  the  single  processes 
occurring  in  the  animal  body  or  in  the  explanation  of 
the  functions  of  the  individual  organs.     Nobody,  not 


2  Introductory  Remarks 

even  a  scientific  vitalist,  would  think  of  treating  the 
process  of  digestion,  metabolism,  production  of  heat, 
and  electricity  or  even  secretion  or  muscular  contrac- 
tion in  any  other  than  a  purely  chemical  or  physico- 
chemical  way;  nor  would  anybody  think  of  explaining 
the  functions  of  the  eye  or  the  ear  from  any  other 
standpoint  than  that  of  physics. 

When  the  actions  of  the  organism  as  a  whole  are  con- 
cerned, we  find  a  totally  different  situation.  The  same 
physiologists  who  in  the  explanation  of  the  individ- 
ual processes  would  follow  the  strictly  physicochemi- 
cal  viewpoint  and  method  would  consider  the  reactions 
of  the  organism  as  a  whole  as  the  expression  of  non- 
physical  agencies.  Thus  Claude  Bernard,^  who  in 
the  investigation  of  the  individual  life  processes  was  a 
strict  mechanist,  declares  that  the  making  of  a  har- 
monious organism  from  the  egg  cannot  be  explained 
on  a  mechanistic  basis  but  only  on  the  assumption  of 
a  "directive  force."  Bernard  assumes,  as  Bichat  and 
others  had  done  before  him,  that  there  are  two  opposite 
processes  going  on  in  the  living  organism :  (i)  the  pheno- 
mena of  vital  creation  or  organizing  synthesis ;  (2)  the 
phenomena  of  death  or  organic  destruction.  It  is  only 
the  destructive  processes  which  give  rise  to  the  physical 
manifestations  by  which  we  judge  life,  such  as  respira- 
tion and  circulation  or  the  activity  of  glands,  and  so  on. 

'  Bernard  C,  LefOrtJ  sur  les  Phenomenes  de  la  Vie.  Paris,  1885,  i., 
22-64, 


Introductory  Remarks  3 

The  work  of  creation  takes  place  unseen  by  us  in  the 
egg  when  the  embryo  or  organism  is  formed.  This 
vital  creation  occurs  always  according  to  a  definite 
plan,  and  in  the  opinion  of  Bernard  it  is  impossible 
to  account  for  this  plan  on  a  purely  physicochemical 
basis. 

There  is  so  to  speak  a  pre-established  design  of  each  being 
and  of  each  organ  of  "such  a  kind  that  each  phenomenon  by 
itself  depends  upon  the  general  forces  of  nature,  but  when 
taken  in  connection  with  the  others  it  seems  directed  by 
some  invisible  guide  on  the  road  it  follows  and  led  to  the 
place  it  occupies.  .  .  . 

We  admit  that  the  life  phenomena  are  attached  to  physico- 
chemical  manifestations,  but  it  is  true  that  the  essential 
is  not  explained  thereby;  for  no  fortuitous  coming  together 
of  physicochemical  phenomena  constructs  each  organism 
after  a  plan  and  a  fixed  design  (which  are  foreseen  in  ad- 
vance) and  arouses  the  admirable  subordination  and  har- 
monious agreement  of  the  acts  of  life.  .  .  . 

We  can  only  know  the  material  conditions  and  not  the 
intimate  nature  of  life  phenomena.  We  have  therefore 
only  to  deal  with  matter  and  not  with  the  first  causes  or 
the  vital  force  derived  therefrom.  These  causes  are  inacces- 
sible to  us,  and  if  we  believe  anything  else  we  commit  an 
error  and  become  the  dupes  of  metaphors  and  take  figura- 
tive language  as  real.  .  .  .  Determinism  can  never  be  but 
physicochemical  determinism.  The  vital  force  and  life 
belong  to  the  metaphysical  world. 

In  other  words,  Bernard  thinks  it  his  task  to  account 
for  individual  life  phenomena  on  a  purely  physico- 
chemical  basis — but  the  harmonious  character  of  the 


4  Introductory  Remarks 

organism  as  a  whole  is  in  his  opinion  not  produced  by 
the  same  forces  and  he  considers  it  impossible  and 
hopeless  to  investigate  the  "design."  This  attitude 
of  Bernard  would  be  incomprehensible  were  it  not  for 
the  fact  that,  when  he  made  these  statements,  the 
phenomena  of  specificity,  the  physiology  of  develop- 
ment and  regeneration,  the  Mendelian  laws  of  heredity, 
the  animal  tropisms  and  their  bearing  on  the  theory 
of  adaptation  were  unknown. 

This  explanation  of  Bernard's  attitude  is  apparently 
contradicted  by  the  fact  that  Driesch^  and  v.  Uexkull,' 
both  brilliant  biologists,  occupy  today  a  standpoint 
not  very  different  from  that  of  Claude  Bernard.  Driesch 
assumes  that  there  is  an  Aristotelian  "entelechy" 
acting  as  directing  guide  in  each  organism;  and 
V.  Uexkull  suggests  a  kind  of  Platonic  "idea"  as  a 
peculiar  characteristic  of  life  which  accounts  for  the 
purposeful  character  of  the  organism. 

V.  Uexkull  supposes  as  did  Claude  Bernard  and  as 
does  Driesch  that  in  an  organism  or  an  egg  the  ulti- 
mate processes  are  purely  physicochemical.  In  an 
egg  these  processes  are  guided  into  definite  parts 
of  the  future  embryo  by  the  Mendelian  factors  of 
heredity — the  so-called  genes.  These  genes  he  compares 
to  the  foremen  for  the  different  types  of  work  to  be 

*  Driesch,  H.,  The  Science  and  Philosophy  of  the  Organism.  2  vols. 
The  Gififord  Lectures,  1907  and  1908. 

'V.  Uexkull,  J.,  Bausteine  zu  einer  biologischen  Weltanschauung. 
Munchen,  19 13. 


Introductory  Remarks  5 

done  in  a  building.  But  there  must  be  something 
that  makes  of  the  work  of  the  single  genes  a  harmonious 
whole,  and  for  this  purpose  he  assumes  the  existence 
of  "supergenes."^  v.  Uexkull's  ideas  concerning  the 
nature  of  a  Mendelian  factor  and  of  the  "super- 
genes"  are  expressed  in  metaphorical  terms  and  the 
assumption  of  the  "supergenes"  begs  the  question. 
The  writer  is  under  the  impression  that  this  author 
was  led  to  his  views  by  the  beHef  that  the  egg  is  entirely 
undifferentiated.  But  the  unfertilized  egg  is  not  homo- 
geneous, on  the  contrary,  it  has  a  simple  but  definite 
physicochemical  structure  which  suffices  to  determine 
the  first  steps  in  the  differentiation  of  the  organism. 
Of  course,  if  we  suppose  as  do  v.  Uexkull  and  Driesch 
that  the  egg  has  no  structure,  the  development  of 
structure  becomes  a  difficult  problem — but  this  is  not 
the  real  situation. 

2.  Claude  Bernard  does  not  mention  the  possibility 
of  explaining  the  harmony  or  apparent  design  in  the 
organism  on  the  basis  of  the  theory  of  evolution,  he 
simply  considers  the  problem  as  outside  of  biology. 
It  was  probably  clear  to  him  as  it  must  be  to  everyone 
with  an  adequate  training  in  physics  that  natural 
selection  does  not  explain  the  origin  of  variation. 
Driesch  and  v.  Uexkull  consider  the  Darwinian  theory 
a  failure.     We  may  admit  that  the  theory  of  a  forma- 

^  V.  Uexkull,  J.,  Bausteine  zu  einer  hiologischen  Weltanschauung. 
Munchen,  1913,  p.  216. 


6  Introductory  Remarks 

tion  of  new  species  by  the  cumulative  effect  of  aimless 
fluctuating  variations  is  not  tenable  because  fluctuating 
variation  is  not  hereditary ;  but  this  would  only  demand 
a  slight  change  in  the  theory;  namely  a  replacement  of 
the  influence  of  fluctuating  variation  by  that  of  equally 
aimless  mutations.  "With  this  slight  modification  which 
is  proposed  by  de  Vries,  ^  Darwin's  theory  still  serves 
the  purpose  of  explaining  how  without  any  pre-estab- 
lished plan  only  purposeful  and  harmonious  organisms 
should  have  survived.  It  must  be  said,  however, 
that  any  theory  of  life  phenomena  must  be  based  on 
our  knowledge  of  the  physicochemical  constitution  of 
living  matter,  and  neither  Darwin  nor  Lamarck  was 
concerned  with  this.  Moreover,  we  cannot  consider 
any  theory  of  evolution  as  proved  unless  it  permits  us 
to  transform  at  desire  one  species  into  another,  and 
this  has  not  yet  been  accomplished. 

It  may  be  of  some  interest  to  point  out  that  we  do 
not  need  to  make  any  definite  assumption  concerning 
the  mechanism  of  evolution  and  that  we  may  yet  be 
able  to  account  for  the  fact  that  the  surviving  organ- 
isms are  to  all  appearances  harmonious.  The  writer 
pointed  out  that  of  all  the  100,000,000  conceivable 
crosses  of  teleost  fish  (many  of  which  are  possible) 
not  many  more  than  10,000,  i.  e.,  about  one-hundredth 
of  one  per  cent.,  are  able  to  live  and  propagate.  Those 
that  live  and  develop  are  free  from  the  grosser  type 

'  de  Vries,  H.,  Die  Mutationstheorie.     Leipzig,  1901. 


Introductory  Remarks  7 

of  disharmonies,  the  rest  are  doomed  on  account  of  a 
gross  lack  of  harmony  of  the  parts.  These  latter  we 
never  see  and  this  gives  us  the  erroneous  conception 
that  harmony  or  "design"  is  a  general  character  of 
Hving  matter.  If  anybody  wishes  to  call  the  non- 
viability  of  99rifo  per  cent,  of  possible  teleosts  a  pro- 
cess of  weeding  out  by  "natural  selection"  we  shall 
raise  no  objection,  but  only  wish  to  point  out  that  our 
way  of  explaining  the  lack  of  design  in  living  nature 
would  be  valid  even  if  there  were  no  theory  of  evolu- 
tion or  if  there  had  never  been  any  evolution. 

3.  V.  Uexkull  is  perfectly  right  in  connecting 
the  problem  of  design  in  an  organism  with  Mendelian 
heredity.  The  work  on  Mendelian  heredity  has  shown 
that  an  extremely  large  number  of  independently 
transmissible  Mendelian  factors  help  to  shape  the 
individual.  It  is  not  yet  proven  that  the  organism 
is  nothing  but  a  mosaic  of  Mendelian  factors,  but  no 
writer  can  be  blamed  for  considering  such  a  possibility. 
If  we  assume  that  the  organism  is  nothing  but  a  mosaic 
of  Mendelian  characters  it  is  difficult  indeed  to  under- 
stand how  they  can  force  each  other  into  a  harmonious 
whole  ^;  even  if  we  make  ample  allowance  for  the  law 

'  This  difSculty  is  also  felt  by  mechanistic  writers  like  Child,  who 
on  page  12  of  his  recent  book  on  Senescence  and  Rejuvenescence 
(Chicago,  1915)  makes  the  following  remarks:  "These  theories  of  Weis- 
mann  do  not  account  satisfactorily  for  the  peculiarly  constant  course 
and  character  of  development  and  morphogenesis.  If  we  follow  them 
to  their  logical  conclusion,  which  their  authors  have  not  done,  we  find 
ourselves  forced  to  assume  the  existence  of  some  sort  of  controlling  and 


8  Introductory  Remarks 

of  chance  and  the  corresponding  wastefulness  in  the 
world  of  the  living.  But  it  is  doubtful  whether  this 
idea  of  the  role  of  Mendelian  factors  is  correct.  The 
facts  of  experimental  embryology  strongly  indicate 
the  possibility  that  the  cytoplasm  of  the  egg  is  the 
future  embryo  (in  the  rough)  and  that  the  Mendelian 
factors  only  impress  the  individual  (and  variety)  char- 
acters upon  this  rough  block.  This  idea  is  supported 
by  the  fact  that  the  first  development — in  the  sea 
urchin  to  the  gastrula  stage  inclusive — is  independent 
of  the  nucleus,  which  is  the  bearer  of  the  Mendelian 
factors.  Not  before  the  skeleton  or  mesenchyme  is 
formed  in  the  sea  urchin  egg  is  the  influence  of  the 
nucleus  noticeable.  This  has  been  shown  in  the  ex- 
periments of  Boveri  in  which  an  enucleated  fragment  of 
an  egg  was  fertilized  with  a  spermatozoon  of  a  foreign 
species.  If  this  is  generally  true,  it  is  conceivable  that 
the  generic  and  possibly  also  the  species  characters 
of  organisms  are  determined  by  the  cytoplasm  of  the 
egg  and  not  by  the  Mendelian  factors. 


co-ordinating  principle  outside  the  units  themselves  and  superior  to 
them.  If  the  units  constitute  the  physicochemical  basis  of  life,  as 
their  authors  maintain,  then  this  controlling  principle,  since  it  is  an 
essential  feature  of  life,  must  of  necessity  be  something  which  is  not 
physicochemical  in  nature.  In  short  these  theories  lead  us  in  the  final 
analysis  to  the  same  conclusion  as  that  reached  by  the  neovitalists. 
If  we  are  not  content  to  accept  this  conclusion  we  must  reject  the 
theories."  These  last  sentences  do  not  exhaust  all  the  possibilities, 
since  the  writer  is  trying  to  show  in  this  book  that  the  widest  accept- 
ance of  the  chromosome  theory  of  heredity  is  compatible  with  a  con- 
sistent physicochemical  conception  of  the  organism  as  a  whole. 


Introductory  Remarks  9 

In  any  case,  we  can  state  today  that  the  cytoplasm 
contains  the  rough  preformation  of  the  future  embryo. 
This  would  show  then  that  the  idea  of  the  organism 
being  a  mosaic  of  Mendelian  characters  which  have 
to  be  put  into  place  by  "supergenes"  is  unnecessary. 
If  the  egg  is  already  the  embryo  in  the  rough  we  can 
imagine  the  Mendelian  factors  as  giving  rise  to  specific 
substances  which  go  into  the  circulation  and  start  or 
accelerate  different  chemical  reactions  in  different 
parts  of  the  embryo,  and  thereby  call  forth  the  finer 
details  characteristic  of  the  variety  and  the  individual. 
The  idea  that  the  egg  is  the  future  embryo  is  supported 
by  the  fact  that  we  can  call  forth  a  normal  organism 
from  an  unfertilized  egg  by  artificial  means;  while  it  is 
apparently  impossible  to  cause  the  spermatozoon  to 
develop  into  an  organism  outside  the  egg. 

4.  The  influence  of  the  whole  on  the  parts  is  no- 
where shown  more  strikingly  than  in  the  field  of  re- 
generation. It  is  known  that  pieces  cut  from  the  plant 
or  animal  may  give  rise  to  new  growth  which  in  many 
cases  will  restore  somewhat  the  original  organism. 
Instead  of  asking  what  is  the  cause  of  this  so-called 
regeneration  we  may  ask,  why  the  same  pieces  do  not 
regenerate  as  long  as  they  are  parts  of  the  whole.  In 
this  form  the  mysterious  influence  of  the  whole  over 
its  parts  is  put  into  the  foreground.  We  shall  see  that 
growth  takes  place  in  certain  cells  when  certain  sub- 
stances   in    the    circulation    can    collect    there.     The 


10  Introductory  Remarks 

mysterious  influence  of  the  whole  on  these  parts  con- 
sists often  merely  of  the  fact  that  the  circulating  speci- 
fic or  non-specific  substances — we  cannot  yet  decide 
which — will  in  the  whole  be  attracted  by  certain  spots 
and  that  this  will  prevent  them  from  acting  on  other 
parts  of  the  organism.  If  such  parts  are  isolated  the 
substances  can  no  longer  flow  away  from  these  parts 
and  the  parts  will  begin  to  grow.  It  thus  becomes 
utterly  unnecessary  to  endow  such  organisms  with  a 
"directing  force"  which  has  to  elaborate  the  isolated 
parts  into  a  whole. 

5.  The  same  difficulty  which  we  have  discussed  in 
regard  to  morphogenesis  exists  also  in  connection  with 
those  instincts  which  preserve  the  life  of  the  organism 
and  of  the  race.  The  reader  need  only  be  reminded  of 
all  the  complicated  instincts  of  mating  by  which  sperm 
and  eggs  are  brought  together;  or  those  by  which  the 
young  are  prevented  from  starvation  to  realize  the 
apparently  desperate  problems  in  store  for  a  mechanist, 
to  whom  the  assumption  of  design  is  meaningless. 
And  yet  we  are  better  off  in  regard  to  our  knowledge 
of  the  instincts  than  we  are  in  regard  to  morphogenesis, 
as  in  the  former  we  can  show  that  the  apparent  instincts 
in  some  cases  obey  simple  physicochemical  laws  with 
almost  mathematical  accuracy.  Since  the  validity  of 
the  law  of  gravitation  has  been  proved  for  the  solar 
system  the  idea  of  design  in  the  motion  of  the  planets 
has  lost  its  usefulness,  and  this  fact  must  serve  us  as 


Introductory  Remarks  ii 

a  guide  wherever  we  attempt  to  put  science  beyond  the 
possibility  of  mysticism.  As  soon  as  we  can  show  that 
a  Hfe  phenomenon  obeys  a  simple  physical  law  there 
is  no  longer  any  need  for  assuming  the  action  of  non- 
physical  agencies.  We  shall  see  that  this  has  been 
accomplished  for  one  group  of  animal  instincts ;  namely 
those  which  determine  the  relation  of  animals  to  light, 
since  these  are  being  gradually  reduced  to  the  law  of 
Bunsen  and  Roscoe.  This  law  states  that  the  chemical 
effect  of  light  equals  the  product  of  intensity  into  dura- 
tion of  illumination.  Some  authors  object  to  the 
tendency  toward  reducing  everything  in  biology  to 
mathematical  laws  or  figures;  but  where  would  the 
theory  of  heredity  be  without  figures?  Figures  have 
been  responsible  for  showing  that  the  laws  of  chance 
and  not  of  design  rule  in  heredity.  Biology  will  be 
scientific  only  to  the  extent  that  it  succeeds  in  reducing 
life  phenomena  to  quantitative  laws. 

Those  familiar  with  the  theories  of  evolution  know 
the  extensive  role  ascribed  to  the  adaptations  of  organ- 
isms. The  writer  in  1889  called  attention  to  the  fact 
that  reactions  to  light — e.  g.,  positive  heliotropism — 
are  found  in  organisms  that  never  by  any  chance  make 
use  of  them;  and  later  that  a  great  many  organisms 
show  definite  instinctive  reactions  towards  a  galvanic 
current — galvanotropism — although  no  organism  has 
ever  had  or  ever  will  have  a  chance  to  be  exposed  to 
such  a  current  except  in  laboratory  experiments.     This 


12  Introductory  Remarks 

throws  a  different  light  upon  the  seemingly  purposeful 
character  of  animal  reactions.  Heliotropism  depends 
primarily  upon  the  presence  of  photosensitive  sub- 
stances in  the  eye  or  the  epidermis  of  the  organism, 
and  these  substances  are  inherited  regardless  of  whether 
they  are  useful  or  not.  It  is  only  a  metaphor  to  call 
reactions  resulting  from  the  presence  of  photosensitive 
substances  ' '  adaptation. ' '  In  this  book  other  examples 
are  given  which  show  that  authors  have  too  often 
spoken  of  adaptation  to  environment  where  the  en- 
vironment was  not  responsible  for  the  phenomena. 
The  blindness  of  cave  animals  and  the  resistance  of 
certain  marine  animals  to  higher  concentrations  of  sea 
water  are  such  cases.  Cuenot  speaks  of  "preadapta- 
tion" to  express  this  relation.  The  fact  is  that  the 
"adaptations"  often  existed  before  the  animal  was 
exposed  to  surroundings  where  they  were  of  use.  This 
relieves  us  also  of  the  necessity  of  postulating  the 
existence  of  the  inheritance  of  acquired  characters, 
although  it  is  quite  possible  that  the  future  may  furnish 
proof  that  such  a  mode  of  inheritance  exists. 

6.  We  have  mentioned  that  according  to  Claude 
Bernard  two  groups  of  phenomena  occur  in  the  living 
organism:  (l)  the  phenomena  of  vital  creation  or  or- 
ganizing synthesis  (especially  in  the  egg  and  during 
development);  (2)  the  phenomena  of  death  or  organic 
destruction.  These  two  processes  are  briefly  discussed 
in  the  first  and  last  chapters. 


Introductory  Remarks  13 

These  introductory  remarks  may  perhaps  make  it 
easier  for  the  reader  to  retain  the  thread  of  the  main 
ideas  in  the  details  of  experiments  and  tables  given  in 
this  book. 


CHAPTER  II 

THE  SPECIFIC  DIFFERENCE  BETWEEN  LIVING  AND  DEAD 

MATTER    AND    THE    QUESTION    OF    THE    ORIGIN 

OF   LIFE 

/  I.  Each  organism  is  characterized  by  a  definite 
rform  and  we  shall  see  in  the  next  chapter  that  this  form 
is  determined  by  definite  chemical  substances.  The 
same  is  true  for  crystals,  where  substance  and  form  are 
definitely  connected  and  there  are  further  analogies 
between  organisms  and  crystals.  Crystals  can  grow 
in  a  proper  solution,  and  can  regenerate  their  form  in 
such  a  solution  when  broken  or  injured;  it  is  even 
possible  to  prevent  or  retard  the  formation  of  crystals 
in  a  supersaturated  solution  by  preventing  "germs" 
in  the  air  from  getting  into  the  solution,  an  observation 
which  was  later  utilized  by  Schroeder  and  Pasteur  in 
their  experiments  on  spontaneous  generation.  How- 
ever, the  analogies  between  a  living  organism  and  a 
crystal  are  merely  superficial  and  it  is  by  pointing  out 
the  fundamental  differences  between  the  behaviour  cf 
crystals  and  that  of  living  organisms  that  we  can  best 

14 


The  Origin  of  Life  15 

understand  the  specific  difference  between  non-living 
and  living  matter.  It  is  true  that  a  crystal  can  grow, 
but  it  will  do  so  only  in  a  supersaturated  solution  of 
its  own  substance.  Just  the  reverse  is  true  for  living 
organisms.  In  order  to  make  bacteria  or  the  cells  of 
our  body  grow,  solutions  of  the  split  products  of  the 
substances  composing  them  and  not  the  substances 
themselves  must  be  available  to  the  cells ;  second,  these 
solutions  must  not  be  supersaturated,  on  the  contrary, 
they  must  be  dilute;  and  third,  growth  leads  in  living 
organisms  to  cell  division  as  soon  as  the  mass  of  the 
cell  reaches  a  certain  hmit.  This  process  of  cell  divi- 
sion cannot  be  claimed  even  metaphorically  to  exist  in 
a  crystal.  A  correct  appreciation  of  these  facts  will 
give  us  an  insight  into  the  specific  difference  between 
non-living  and  living  matter.  The  formation  of  living 
matter  consists  in  the  synthesis  of  the  proteins,  nucleins, 
fats,  and  carbohydrates  of  the  cells,  from  the  split  pro- 
ducts. To  give  an  historical  example,  Pasteur  showed 
that  yeast  cells  and  other  fungi  could  be  raised  on  the 
following  sterilized  solution :  water,  100  gm.,  crystallized 
sugar,  10  gm.,  ammonium  tartrate,  0.2  gm.  to  0.5  gm., 
and  fused  ash  from  yeast,  o.i  gm.  ^  He  undertook  this 
experiment  to  disprove  the  idea  that  protein  or  organic 
matter  in  a  state  of  decomposition  was  needed  for  the 
origin  of  new  organisms  as  the  defenders  of  the  idea 
of  spontaneous  generation  had  maintained. 

^  Pasteur,  L.,  Annal.  d.  Chim.  et  d.  Physique,  1862,  3  ser.,  Ixiv.,  i. 


1 6  Living  and  Dead  Matter  and 

2.  That  such  a  solution  can  serve  for  the  synthesis 
of  all  the  compounds  of  living  yeast  cells  is  due  to  the 
fact  that  it  contains  the  sugars.  From  the  sugars 
organic  acids  can  be  formed  and  these  with  ammonia 
(which  was  offered  in  the  form  of  ammonium  tartrate) 
may  give  rise  to  the  formation  of  amino  acids,  the 
"building  stones"  of  the  proteins.  It  is  thus  obvious 
that  the  synthesis  of  living  matter  centres  around  the 
sugar  molecule.  The  phosphates  are  required  for  the 
formation  of  the  nucleins,  and  the  work  of  Harden  and 
Young  suggests  that  they  play  also  a  role  in  the  alco- 
holic fermentation  of  sugar. 

Chlorophyll,  under  the  influence  of  the  red  rays  of 
light,  manufactures  the  sugars  from  the  CO  2  of  the  air. 
This  makes  it  appear  as  though  life  on  our  planet  should 
have  been  preceded  by  the  existence  of  chlorophyll, 
a  fact  difficult  to  understand  since  it  seems  more  natural 
to  conceive  of  chlorophyll  as  a  part  or  a  product  of 
living  organisms  rather  than  the  reverse.  Where  then 
should  the  sugar  come  from,  which  is  a  constituent  of 
the  majority  of  culture  media  and  which  seems  a  pre-/ 
requisite  for  the  synthesis  of  proteins  in  living  organ- 
isms? 

The  investigations  of  Winogradsky  on  nitrifying,^ 
sulphur  and  perhaps  also  on  iron  bacteria  have  to  all 
appearances  pointed  a  way  out  of  this  difficulty.     It 

'Winogradsky,  S.,  "Die  Nitrification,"  Handh.  d.  tech.  Mykol.,  1904- 
06,  iii.,  132. 


The  Origin  of  Life  17 

seemed  probable  that  there  were  specific  micro-organ- 
isms which  oxidized  the  ammonia  formed  in  sewage 
or  in  the  putrefaction  of  Hving  matter,  but  the  attempts 
to  prove  this  assumption  by  raising  such  a  nitrifying 
micro-organism  on  one  of  the  usual  culture  media,  all 
of  which  contained  organic  compounds,  failed.  Led 
by  the  results  of  his  observations  on  sulphur  bacteria 
it  occurred  to  Winogradsky  that  the  presence  of  organic 
compounds  stood  in  the  way  of  raising  these  bacteria, 
and  this  idea  proved  correct.  The  bacteria  oxidizing  am- 
monia to  nitrites  were  grown  on  the  following  medium ; 
I  gm.  ammonium  sulphate,  i  gm.  potassium  phosphate, 
I  gm.  magnesium  carbonate,  to  i  litre  of  water.  From 
this  medium,  which  is  free  from  sugar  and  contains 
only  constituents  which  could  exist  on  the  planet  before 
the  appearance  of  life,  the  nitrifying  bacteria  were  able 
to  form  sugars,  fatty  acids,  proteins,  and  the  other 
specific  constituents  of  living  matter.  Winogradsky 
proved,  by  quantitative  determination,  that  with  the 
nitrification  an  increase  in  the  amount  of  carbon  com- 
pounds takes  place.  "Since  this  bound  carbon  in  the 
cultures  can  have  no  other  source  than  the  CO  2  and 
since  the  process  itself  can  have  no  other  cause  than 
the  activity  of  the  nitrifying  organism,  no  other  alter- 
native was  left  but  to  ascribe  to  it  the  power  of  assimi- 
lating CO 2."^  "Since  the  oxidation  of  NH3  is  the 
only  source  of  chemical  energy  which  the  nitrifying 

"  Winogradsky,  loc.  ciL,  p.  163  and  ff. 


i8  Living  and  Dead  Matter  and 

organism  can  use  it  was  clear  a  priori  that  the  yield 
in  assimilation  must  correspond  to  the  quantity  of  oxi- 
dized nitrogen.  It  turned  out  that  an  approximately 
constant  ratio  exists  between  the  values  of  assimi- 
lated carbon  and  those  of  oxidized  nitrogen."  This  is 
illustrated  by  the  results  of  various  experiments  as 
shown  in  Table  I. 

TABLE  I 


No.  5 

No.  6 

No.  7 

No.  8 

Oxidized  N 

mg. 

722.0 
19.7 

mg. 
506.1 

15-2 

mg. 

928.3 
26.4 

mg. 

815.4 
22.4 

Assimilated  C 

Ratio  N:  C 

36.6 

33-3 

35-2 

36.4 

It  is  obvious  that  i  part  of  assimilated  carbon 
corresponds  to  about  35.4  parts  oxidized  nitrogen  or 
96  parts  of  nitrous  acid. 

These  results  of  Winogradsky  were  confirmed  in  very 
careful  experiments  by  E.  Godlewski,  Sr. ' 

The  nitrites  are  further  oxidized  by  another  kind  of 
micro-organisms  into  nitrates  and  they  also  can  be 
raised  without  organic  material. 

Winogradsky  had  already  previously  discovered  that 

'Godlewski,  E.,  Anz.  d.  Akad.  d.  Wissersch.  in  Krakau,  1892,  408; 
1895,  178. 


The  Origin  of  Life  19 

the  hydrogen  sulphide  which  is  formed  as  a  reduction 
product  from  CaS04  or  in  putrefaction  by  the  activity 
of  certain  bacteria  can  be  oxidized  by  certain  groups 
of  bacteria,  the  sulphur  bacteria.  Such  bacteria,  e.  g., 
Beggiatoa,  are  also  commonly  found  at  the  outlet  of 
sulphur  springs.  They  utilize  the  hydrogen  sulphide 
which  they  oxidize  to  sulphur  and  afterwards  to 
sulphates,  according  to  the  scheme : 

(i)  2H,S  +  0.=2H,0+S, 
(2)  S,+30,+2H,0  =  2H,S04 

The  sulphuric  acid  is  at  once  neutralized  by  car- 
bonates. 

Winogradsky  assumes  that  the  oxidation  of  H^S  by 
the  sulphur  bacteria  is  the  source  of  energy  which  plays 
the  same  role  as  the  oxidation  of  NH3  plays  in  the 
nitrifying  bacteria,  or  the  oxidation  of  carbon  compounds 
• — sugar  and  others — in  the  case  of  the  other  lower  and 
higher  organisms.  Winogradsky  has  made  it  very 
probable  that  sulphur  bacteria  do  not  need  any  organic 
compounds  and  that  their  nutrition  may  be  accom- 
plished with  a  purely  mineral  culture  medium,  like 
that  of  the  nitrite  bacteria.  On  the  basis  of  this  assump- 
tion they  should  also  be  able  to  form  sugars  from  the 
CO  2  of  the  air. 

Nathanson  ^  discovered  in  the  sea  water  the  existence 

'  Nathanson,  Mitteil.  d.  zool.  Station,  Neapel,  1902, 


20  Living  and  Dead  Matter  and 

of  bacteria  which  oxidize  thiosulphate  to  sulphuric 
acid.  They  will  develop  if  some  Na2S203  is  added  to 
sea  water.  These  bacteria  can  only  develop  if  COj 
from  the  air  is  admitted  or  when  carbonates  are  pre- 
sent. For  these  organisms  the  CO  2  cannot  be  replaced 
by  glucose,  urea,  or  other  organic  substances.  Such 
bacteria  must  therefore  possess  the  power  of  producing 
sugar  and  starch  from  CO  2  without  the  aid  of  chloro- 
phyll. Similar  observations  were  made  by  Beijerinck 
on  a  species  of  fresh-water  bacteria.  ^ 

Finally  the  case  of  iron  bacteria  may  briefly  be 
mentioned  though  Winogradsky's  views  are  not  accepted 
by  Molisch. 

We  may,  therefore,  consider  it  an  estabhshed  fact 
that  there  are  a  number  of  organisms  which  could 
have  lived  on  this  planet  at  a  time  when  only  mineral 
constituents,  such  as  phosphates,  K,  Mg,  SO 4,  CO  2, 
and  O2  besides  NH3,  or  SH2,  existed.  This  would 
lead  us  to  consider  it  possible  that  the  first  or- 
ganisms on  this  planet  may  have  belonged  to  that 
world  of  micro-organisms  which  was  discovered  by 
Winogradsky. 

If  we  can  conceive  of  this  group  of  organisms  as 
producing  sugar,  which  in  fact  they  do,  they  could 
have  served  as  a  basis  for  the  development  of  other 
forms  which  require  organic  material  for  their  develop- 
ment. 

*  Beijerinck,  M.,  Folia  Microhiologica,  1914,  iii.,  91. 


The  Origin  of  Life  21 


o 


In  1883  the  small  island  of  Krakatau  was  destroyed 
by  the  most  violent  volcanic  eruption  on  record.  A 
visit  to  the  islands  two  months  after  the  eruption 
showed  that  "the  three  islands  were  covered  with 
pumice  and  layers  of  ash  reaching  on  an  average  a 
thickness  of  thirty  metres  and  frequently  sixty  metres. ' ' "" 
Of  course  all  life  on  the  islands  was  extinct.  When 
Treub  in  1886  first  visited  the  island,  he  found  that 
blue-green  algss  were  the  first  colonists  on  the  pumice 
and  on  the  exposed  blocks  of  rock  in  the  ravines  on 
the  mountain  slopes.  Investigations  made  during 
subsequent  expeditions  demonstrated  the  association 
of  diatoms  and  bacteria.  All  of  these  were  probably 
carried  by  the  wind.  The  algffi  referred  to  were  accord- 
ing to  Euler  of  the  nostoc  type.  Nostoc  does  not  re- 
quire sugar,  since  it  can  produce  that  compound  from 
the  CO  2  of  the  air  by  the  activity  of  its  chlorophyll. 
This  organism  possesses  also  the  power  of  assimilating 
the  free  nitrogen  of  the  air.  From  these  observations 
and  because  the  NostocacecB  generally  appear  as  the 
first  settlers  on  sand  the  conclusion  has  been  drawn 
that  they  or  the  group  of  Schizophycece  to  which  they 
belong  formed  the  first  settlers  of  our  planet.^  This 
conclusion  is  not  quite  safe  since  in  the  settlement  of 
Krakatau  as  well   as   in   the  first   colonizing  of  sand 

^  Ernst,  A.,  The  New  Flora  of  the  Volcanic  Island  of  Krakatau, 
Cambridge,  1908. 

^  Euler,  H.,  Pflanzenchemie,  1909,  ii.  and  iii.,  140. 


22  Living  and  Dead  Matter  and 

areas  the  nature  of  the  first  settler  is  determined 
chiefly  by  the  carrying  power  of  wind  (or  waves  and 
birds). 

We  may  now  return  from  this  digression  to  the  real 
object  of  our  discussion,  namely  that  the  nutritive 
solutions  of  organisms  must  be  very  dilute  and  consist 
of  the  split  products  of  the  complicated  compounds 
of  which  the  organisms  consist.  The  examples  given 
sufficiently  illustrate  this  statement. 

The  nutritive  medium  of  our  body  cells  is  the  blood, 
and  while  we  take  up  as  food  the  complicated  com- 
pounds of  plants  or  animals,  these  substances  undergo 
a  digestion,  i.  e.,  a  splitting  up  into  small  constituents 
before  they  can  diffuse  from  the  intestine  into  the  blood. 
Thus  the  proteins  are  digested  down  to  the  amino 
acids  and  these  diffuse  into  the  blood  as  demonstrated 
by  Folin  and  by  Van  Slyke.  From  here  the  cells  take 
them  up.  The  different  proteins  differ  in  regard  to 
the  different  types  of  amino  acids  which  they  contain. 
While  the  bacteria  and  fungi  and  apparently  the  higher 
plants  can  build  up  all  their  different  amino  acids  from 
ammonia,  this  power  is  no  longer  found  in  the  mammals 
which  can  form  only  certain  amino  acids  in  their  body 
and  must  receive  the  others  through  their  food.  As 
a  consequence  it  is  usually  necessary  to  feed  young 
animals  on  more  than  one  protein  in  order  to  make 
them  grow,  since  one  protein,  as  a  rule,  does  not  contain 
all  the  amino  acids  needed  for  the  manufacture  of  all 


The  Origin  of  Life  23 

the  proteins  required  for  the  formation  of  the  material 
of  a  growing  animal.  ^ 

3.  The  essential  difference  between  living  and  non- 
living matter  consists  then  in  this:  the  living  cell  syn- 
thetizes  its  own  complicated  specific  material  from 
indifferent  or  non-specific  simple  compounds  of  the 
surrounding  medium,  while  the  crystal  simply  adds 
the  molecules  found  in  its  supersaturated  solution. 
This  synthetic  power  of  transforming  small  "building 
stones"  into  the  complicated  compounds  specific  for 
each  organism  is  the  "secret  of  Hfe"  or  rather  one  of 
the  secrets  of  life. 

What  clew  have  we  in  regard  to  the  nature  of  this 
synthetic  power?  We  know  that  the  comparatively 
great  velocity  of  chemical  reactions  in  a  living  organism 
is  due  to  the  presence  of  enzymes  (ferments)  or  to 
catalytic  agencies  in  general.  Some  of  these  catalytic 
agencies  are  specific  in  the  sense  that  a  given  catalyzer 
can  accelerate  the  reaction  of  only  one  step  in  a  com- 
plicated chemical  reaction.  While  these  enzymes  are 
formed  by  the  action  of  the  body  they  can  be  separated 
from  the  body  without  losing  their  catalytic  efficiency. 
It  was  a  long  time  before  scientists  succeeded  in  isolat- 
ing the  enzyme  of  the  yeast  cell  which  causes  the  alco- 
holic fermentation  of  sugar;  and  this  gave  rise  to  the 

'  This  fact  was  thoroughly  established  by  Mendel  and  Osborne.  A 
summary  of  their  work  is  given  in  Underbill,  F.  P.,  Physiology  of  the 
Amino  Acids,  1916. 


24  Livinor  and  Dead  Matter  and 


premature  statement  that  it  was  not  possible  to  isolate 
this  enzyme  since  it  was  bound  up  with  the  life  of  the 
yeast  cell.  Such  a  statement  was  even  made  by  a 
man  like  Pasteur,  who  was  usually  a  model  of  restraint 
in  his  utterances,  and  yet  the  work  of  Buchner  proved 
him  to  be  wrong. 

The  general  mechanism  of  the  action  of  the  hydro- 
lyzing  enzymes  is  known.  The  old  idea  of  de  la  Rive, 
that  a  molecule  of  enzyme  combines  transitorily  with 
a  molecule  of  substrate;  the  further  idea,  which  may 
possibly  go  back  to  Engler,  that  the  molecule  of  sub- 
strate is  disrupted  in  the  "strain"  of  the  new  combina- 
tion and  that  the  broken  fragments  fall  off  or  are  easily 
knocked  off  by  collision  from  the  ferment  molecule 
which  is  now  ready  to  repeat  the  process,  seems  to  be 
correct.  On  the  assumption  that  the  velocity  of  en- 
zyme reaction  is  proportional  to  the  mass  of  the  enzyme 
and  that  de  la  Rive's  idea  was  correct,  Van  Slyke  and 
Cullen  were  able  to  calculate  the  coefficients  of  the 
velocity  of  enzyme  reactions  for  the  fermentation  of 
urea  and  other  substances,  and  the  agreement  between 
calculated  and  observed  values  was  remarkable.  ^ 

While  the  hydrolytic  action  of  enzymes  is  thus  clear 
the  synthesis  in  the  cell  is  still  a  riddle.  An  interesting 
suggestion  was  made  by  van't  Hoff,  who  in  1898  ex- 
pressed the  idea  that  the  hydrolytic  enzymes  should 

'  Van  Slyke,  D.  D.,  and  Cullen,  G.  E.,  Jour.  Biol.  Chetn.,  1914,  xix., 
141. 


The  Origin  of  Life  25 

also  act  in  the  opposite  direction,  namely  synthetically. 
Thus  it  should  not  only  be  possible  to  digest  proteins 
with  pepsin  but  also  to  synthetize  them  from  the  pro- 
ducts of  digestion  with  the  aid  of  the  same  enzyme. 
This  expectation  was  based  on  the  idea  that  the  enzyme 
did  not  alter  the  equilibrium  between  the  hydrolyzed 
and  non-hydrolyzed  part  of  the  substrate  but  only 
accelerated  the  rate  with  which  the  equilibrium  was 
reached.  Van't  Hoff 's  idea  omitted,  however,  the  pos- 
sibility that  in  the  transitory  combination  between 
enzyme  molecule  and  substrate  a  change  in  the  molec- 
ular configuration  of  the  substrate  or  in  the  distribution 
of  intramolecular  strain  may  take  place.  The  first 
apparently  complete  confirmation  of  van't  Hoff 's  sug- 
gestion appeared  in  the  form  of  the  synthesis  of  maltose 
from  grape  sugar  by  the  enzyme  maltase,  which  decom- 
poses maltose  into  grape  sugar.  By  adding  the  enzyme 
maltase  from  yeast  to  a  forty  per  cent,  solution  of 
glucose  Croft  HilP  obtained  a  good  yield  of  mal- 
tose. It  turned  out,  however,  that  what  he  took  for 
maltose  was  not  this  compound  but  an  isomer,  name- 
ly isomaltose,  which  has  a  different  molecular  con- 
figuration and  cannot  be  hydrolyzed  by  the  enzyme 
maltase. 

Lactose  is  hydrolyzed  from  kephyr  by  an  enzyme 
lactase  into  galactose  and  glucose;  by  adding  this 
enzyme    to    galactose    and    glucose   a    synthesis   was 

'  Hill,  C,  Jour.  Chem.  Soc,  1898,  Ixxili.,  634. 


26  Living  and  Dead  Matter  and 

obtained  not  of  lactose  but  of  Isolactose;  the  latter, 
however,  is  not  decomposed  by  the  enzyme  lactase. 

E.  F.  Armstrong  has  worked  out  a  theory  which 
tries  to  account  for  this  striking  phenomenon  by  assum- 
ing "that  the  enzyme  has  a  specific  influence  in  pro- 
moting the  formation  of  the  biose  which  it  cannot 
hydrolyze."'  The  theory  is  very  ingenious  and  seems 
supported  by  fact.  This  then  would  lead  to  the  result 
that  certain  hydrolytic  enzymes  may  have  a  synthetic 
action  but  not  in  the  manner  suggested  by  van't  Hofi. 

The  principle  enunciated  by  Armstrong,  that  in  the 
synthetic  action  of  hydrolytic  enzymes  not  the  origi- 
nal compound  but  an  isomer  is  formed  which  can 
not  be  hydrolyzed  by  the  enzyme,  may  possibly  be 
of  great  importance  in  the  understanding  of  life  phe- 
nomena. It  shows  us  how  the  cell  can  grow  in  the 
presence  of  hydrolytic  enzymes  and  why  in  hunger  the 
disintegration  of  the  cell  material  is  so  slow.  It  was 
at  first  thought  that  the  formation  of  isomers  con- 
tradicted the  idea  of  the  reversible  action  of  enzymes, 
but  this  is  not  the  case ;  on  the  contrary,  it  supports  it 
but  makes  an  addition  which  may  solve  the  riddle  of 
what  Claude  Bernard  called  the  creative  action  of 
living  matter.  We  shall  come  back  to  this  problem 
in  the  last  chapter. 

Kastle  and  Loevenhart  demonstrated  the  synthesis 
of  a  trace  of  ethylbutyrate  by  lipase  if  the  latter  enzyme 

'  Armstrong,  E.  F.,  Proc.  Royal  Soc,  1905,  B.  Ixxvi.,  592. 

i 


The  Origin  of  Life  27 

was  added  to  the  products  of  the  hydrolysis  of  ethyl- 
butyrate,  ethyl  alcohol,  and  butyric  acid  by  the  same 
enzyme.^  -Taylor^  obtained  the  synthesis  of  a  sHght 
amount  of  triolein 

by  the  addition  of  the  dried  fat-free  residue  of  the  castor 
bean  to  a  mixture  of  oleinic  acid  and  glycerine.  .  .  .  No 
synthesis  occurred  with  acetic,  butyric,  palmitic,  and 
stearic  acids  with  glycerine,  mannite,  and  dulcite,  and  the 
experiments  with  the  last  two  alcohols  and  oleinic  acid 
likewise  yielded  no  synthesis. 

This  suggests  possibly  a  specific  action  of  the  enzyme. 
If  this  slight  reversible  action  had  any  biological  signi- 
ficance (which  might  be  possible,  since  in  the  organism 
secondary  favourable  conditions  might  be  at  work 
which  are  lacking  in  vitro)  there  should  be  a  parallelism 
between  masses  of  Hpase  in  different  kinds  of  tissues  and 
fat  synthesis.  Loevenhart  indicated  that  this  might 
be  a  fact,  but  a  more  extensive  investigation  by  H.  C. 
Bradley  has  made  this  very  dubious.  ^ 

Very  little  is  known  concerning  the  reversible  action 
of  the  hydrolytic  protein  enzymes.  A.  E.  Taylor 
digested  protamine  sulphate  with  trypsin  and  found 
that  after  adding  trypsin  to  the  products  of  digestion 
a  precipitate  was  formed  after  long  standing;  and  we 

^Kastle,  J.  H.,  and  Loevenhart,  A.  S.,  Am.  Chem.  Jour.,  1900,  xxiv., 
491. 

2 Taylor,  A.  E.,  Univ.  Cal.  Pub.,  1904,  Pathology,  i.,  33;  Jour.  Biol. 
Chem.,  1906,  ii.,  87. 

3  Bradley,  H.  C,  Jour.  Biol.  Chem.,  1913,  xiii.,  407. 


28  Living  and  Dead  Matter  and 

may  also  refer  to  experiments  of  Robertson  with  pepsin 
on  the  products  of  caseinogen  to  which  we  shall  return 
in  the  next  chapter.  It  therefore  looks  at  present  as 
if  van't  Hoff's  idea  of  reversible  enzyme  action  might 
hold  in  the  modification  offered  by  Armstrong.  It 
remains  doubtful,  however,  whether  this  reversibility 
can  explain  all  the  synthetic  processes  in  the  cell.  No 
objection  can  be  offered  at  present  if  any  one  makes 
the  assumption  that  each  cell  has  specific  synthetic 
enzymes  or  some  other  synthetic  mechanisms  which 
are  still  unknown. 

The  mechanisms  for  the  synthesis  of  proteins  must 
have  one  other  peculiarity:  they  must  be  specific  in 
their  action.  We  shall  see  in  the  next  chapter  that 
each  species  seems  to  possess  one  or  more  proteins  not 
found  in  any  other  but  closely  related  species.  Each 
organism  develops  from  a  tiny  microscopic  germ  and 
grows  by  synthetizing  the  non-specific  building  stones 
(amino  acids)  into  the  specific  proteins  of  the  species. 
This  must  be  the  work  of  the  yet  unknown  synthetic 
enzymes  or  mechanisms.  The  elucidation  of  their 
character  would  seem  one  of  the  main  problems  of 
biology.  Needless  to  say  crystallography  is  not  con- 
fronted with  problems  of  such  a  nature. 

The  fact  that  the  living  cell  grows  after  taking  up 
food  has  given  rise  to  curious  misunderstandings. 
Traube  has  shown  that  drops  of  a  liquid  surrounded 
with   a    semipermeable    membrane    may   increase    in 


The  Origin  of  Life  29 

volume  when  put  into  a  solution  of  lower  osmotic 
pressure.  This  has  led  and  is  possibly  still  leading  to 
the  statement  that  the  process  of  growth  by  a  Hving 
cell  has  been  imitated  artificially.  Only  one  feature  has 
been  imitated,  the  increase  in  volume ;  but  the  essential 
feature  of  the  process  in  the  living  cell,  i.  e.,  the  forma- 
tion of  the  specific  constituents  of  the  living  cell  from 
non-specific  products,  has  of  course  not  been  imitated. 
4.  The  constant  synthesis  then  of  specific  material 
from  simple  compounds  of  a  non-specific  character  is 
the  chief  feature  by  which  living  matter  differs  from 
non-living  matter.  With  this  character  is  correlated 
another  one;  namely,  when  the  mass  of  a  cell  reaches 
a  certain  limit  the  cell  divides.  This  is  perhaps  most 
obvious  in  bacteria  which  on  the  proper  nutritive  me- 
dium take  up  food,  grow,  and  divide  into  two  bacteria, 
each  of  which  takes  up  food,  divides,  and  grows  ad 
infinitum,  as  long  as  the  food  lasts,  provided  the  harm- 
ful products  of  metabolism  are  removed.  If  it  be 
true  that  specific  synthetic  ferments  exist  in  each  cell 
it  follows  that  the  cell  must  synthetize  these  also,^ 

^  This  would  lead  to  the  idea  that  the  enzymes  in  the  cell  also  syn- 
thetize molecules  of  their  own  kind,  or  that,  in  other  words,  the  syn- 
thetic processes  in  the  cell  are  of  the  nature  of  autocatalysis.  Loeb, 
Der  chemische  Character  des  Befruchtungsvor gangs,  Leipzig,  1908.  Ro- 
bertson, T.  B.,  Arch.  f.  Entwicklngsmech.,  1908,  xxv.,  581;  xxvi.,  108; 
1913,  xxxvii.,  497;  Am.  Jour.  Physiol.,  1915,  xxxvii.,  i;  Robertson  and 
Wasteneys,  H.,  Arch.  f.  Entwicklngsmech.,  1913,  xxxvii.,  485.  Ostwald, 
Wo.,  Uber  die  zeitlichen  Eigenschaften  der  Entwicklungsvorgdnge,  Leipzig, 
1908. 


30  Living  and  Dead  Matter  and 

as  otherwise  the  synthesis  of  specific  proteins  would 
have  to  come  to  a  standstill. 

This  problem  of  synthesis  leads  to  the  assumption 
of  immortality  of  the  living  cell,  since  there  is  no  a  priori 
reason  why  this  synthesis  should  ever  come  to  a  stand- 
still of  its  own  accord  as  long  as  enough  food  is  avail- 
able and  the  proper  outside  physical  conditions  are 
guaranteed.  It  is  well  known  that  Weismann  has 
claimed  immortality  for  all  unicellular  organisms  and 
for  the  sex  cells  of  metazoa,  while  he  claimed  the  neces- 
sity of  death  for  the  body  cells  of  the  latter.  Leo  Loeb 
was  led  by  his  investigations  on  the  transplanta- 
tion of  cancer  to  assume  immortality  not  only  for 
the  cancer  cell  but  also  for  the  body  cell  of  the 
organism.  He  had  found  in  transplanting  a  malignant 
tumor  from  one  individual  to  another  that  the  tumor 
grew;  that  it  was  not  the  cells  of  the  host  but  the 
transplanted  tumor  cells  of  the  graft  which  grew  and 
multiplied,  and  that  this  process  could  be  repeated  appar- 
ently indefinitely  so  that  it  was  obvious  that  the  trans- 
planted tumor  cells  outlived  the  original  animal.  Such 
experiments  have  since  been  carried  on  so  long  that 
we  may  now  say  that  an  individual  cancer  cell  taken 
from  an  animal  and  transplanted  from  time  to  time 
on  a  new  host  lives  apparently  indefinitely.  Leo  Loeb 
had  found  that  these  tumor  cells  are  simply  modified 
somatic  cells.  He  therefore  suggested  that  the  somatic 
cells  might  be  considered  immortal  with  the  same  right 


The  Origin  of  Life  31 

as  we  speak  of  the  immortality  of  the  germ  cells  of  such 
animals.  ^ 

This  view  receives  its  support  first  from  the  fact  that 
certain  trees  Uke  the  Sequoia  live  several  thousand  years 
and  may  therefore  be  considered  immortal ;  and  second, 

from  the  method  of  tissue  culture.     The  method  of 

# 

cultivating  tissue  cells  in  a  test  tube,  in  the  same  way 
as  is  done  for  bacteria,  was  first  proposed  and  carried 
out  by  Leo  Loeb,  in  1897,^  but  his  test-tube  method 
did  not  permit  the  observation  of  the  transplanted  cell 
under  the  microscope.  This  was  made  possible  by  a 
modification  of  the  method  by  Harrison,  who  established 
the  fact  that  the  axis  cylinder  grows  out  from  the  gan- 
glionic cell.  Harrison  and  Burrows  then  perfected 
the  method  for  the  cultivation  of  the  cells  of  warm- 
blooded animals,  and  with  the  aid  of  these  methods 
Carrel  succeeded  in  keeping  connective-tissue  cells 
of  the  heart  of  an  early  chick  embryo  alive  more 
than  four  years,  and  these  cells  are  still  growing 
and  dividing.  3  Only  very  tiny  masses  of  cells  can 
be  kept  aUve  in  this  way  since  all  the  cells  in  the 
centre  of  a  piece  die  on  account  of  lack  of  oxygen; 


*  Loeb,  Leo,  Jour.  Med.  Res.,  1901,  vi.,  28;  Arch.  f.  Entwicklngsmech., 
1907,  xxiv.,  655. 

^  Loeb,  Leo,  Uber  die  Entstehung  von  Bindegewebe,  Leucocyten  und 
rothen  Blutkorperchen  aus  Epilhel  und  uber  eine  Methode  isolierte  Gewebs- 
teile  zu  zuchten.     Chicago,  1897. 

3  While  this  has  been  demonstrated  thus  far  only  for  connective- 
tissue  cells  it  may  be  true  also  for  other  cells. 


32  Living  and  Dead  Matter  and 

and  every  two  days  a  few  cells  from  the  margin  of 
the  piece  have  to  be  transferred  to  a  new  culture 
medium. 

This  effect  of  lack  of  oxygen  explains  also  why  the 
immortality  of  the  somatic  cells  is  not  obvious.  Death 
in  a  human  being  consists  in  the  stopping  of  heart 
beat  and  respiration,  which  also  terminates  the  action 
of  the  brain  or  at  least  of  consciousness.  Immediately 
after  the  cessation  of  heart  beat  and  respiration  the  cells 
of  muscle  and  of  the  skin  and  probably  many  or  most 
other  organs  are  still  alive  and  might  continue  to  live 
if  transferred  to  another  body  with  circulation  and 
respiration.  As  a  consequence  of  the  lack  of  oxygen 
supply  in  the  dead  body  they  will,  however,  die  com- 
paratively rapidly.  It  may  be  stated  that  hearts  taken 
out  of  the  body  after  a  number  of  hours  can  still  beat 
again  when  put  into  the  proper  solutions  and  upon 
receiving  an  adequate  oxygen  supply. 

The  idea  that  the  body  cells  are  naturally  immortal 
and  die  only  if  exposed  to  extreme  injuries  such  as 
prolonged  lack  of  oxygen  or  too  high  a  temperature 
helps  to  make  one  problem  more  intelligible.  The 
medical  student,  who  for  the  first  time  realizes  that 
life  depends  upon  that  one  organ,  the  heart,  doing  its 
duty  incessantly  for  the  seventy  years  or  so  allotted  to 
man,  is  amazed  at  the  precariousness  of  our  existence. 
It  seems  indeed  uncanny  that  so  delicate  a  mechanism 
should  function  so  regularly  for  so  many  years.     The 


The  Origin  of  Life  33 

mysticism  connected  with  this  and  other  phenomena 
of  adaptation  would  disappear  if  we  coiild  be  certain 
that  all  cells  are  really  immortal  and  that  the  fact  which 
demands  an  explanation  is  not  the  continued  activity 
but  the  cessation  of  activity  in  death.  Thus  we  see 
that  the  idea  of  the  immortality  of  the  body  cell  if  it 
can  be  generalized  may  be  destined  to  become  one  of 
the  main  supports  for  a  complete  physico-chemical 
analysis  of  Hfe  phenomena  since  it  makes  the  durabiHty 
of  organisms  inteUigible. 

5.  This  generalized  idea  of  the  immortality  of  some 
or  possibly  most  or  all  somatic  cells  has  a  bearing  upon 
the  problem  of  the  origin  of  life  on  our  planet.  The 
experiments  of  Spallanzani,  Schwann,  Schroeder,  Pas- 
teur, Tyndall,  and  all  those  who  have  worked  with  pure 
cultures  of  micro-organisms,  have  proved  that  no  spon- 
taneous generation  of  living  from  non-hving  matter 
can  be  demonstrated;  and  the  statements  to  the  con- 
trary were  due  to  experimental  errors  inasmuch  as  the 
new  organisms  formed  were  the  offspring  of  others 
which  had  entered  into  the  culture  medium  by  mistake. 

In  the  last  chapter  of  that  most  fascinating  book 
Worlds  in  the  Making,'^  Arrhenius  discusses  the  possi- 
bility of  life  being  eternal  and  of  living  germs  of  very 
small  dimensions — e.  g.,  the  spores  of  micro-organisms — 
being  carried  through  space  from  one  planet  to  another 

'  Arrhenius,  S.,  Worlds  in  the  Making,  London  and  New  York,  1908, 
p.  212. 
3 


34  Living  and  Dead  Matter  and 

or  even  from  one  solar  system  to  another.  If  it  be 
true  that  there  is  no  spontaneous  generation;  if  it  be 
true  that  all  cells  are  potentially  immortal,  we  may 
indeed  seriously  raise  the  question:  May  not  life  after 
all  be  eternal  ?  Such  ideas  were  advocated  by  Richter 
in  a  rather  phantastic  way  and  more  definitely  by 
Helmholtz  as  well  as  Kelvin.  The  latter  authors 
assumed  that  in  the  collision  of  planets  or  worlds  on 
which  there  is  life,  fragments  containing  living  organ- 
isms will  be  torn  off  and  these  fragments  will  move  as 
seed-bearing  stones  through  space.  "If  at  the  present 
instant  no  life  existed  upon  this  earth,  one  such  stone 
falling  upon  it  might  .  .  .  lead  to  its  becoming  covered 
with  vegetation."  Arrhenius  points  out  the  difficulties 
which  oppose  such  a  view,  as,  e.  g.,  the  fact  "that  the 
meteorite  in  its  fall  towards  the  earth  becomes  incan- 
descent all  over  its  surface  and  any  seeds  on  it  would 
therefore  be  deprived  of  their  germinating  power." 

Arrhenius  suggests  another  and  much  more  ingenious 
idea  based  on  the  fact  that  for  particles  below  a  certain 
size  the  mechanical  pressure  produced  by  light  waves — 
the  radiation  pressure — can  overcome  the  attractive 
force  of  gravitation. 

Bodies  which  according  to  Schwarzschild  would  undergo 
the  strongest  influence  of  solar  radiation  must  have  a  dia- 
meter of  0.00016  mm.  supposing  them  to  be  spherical.  The 
first  question  is  therefore:  Are  there  any  living:  seeds  of 
such  extraordinary  minuteness?     The  reply  of  the  botanist 


The  Origin  of  Life  35 

is  that  spores  of  many  bacteria  have  a  size  of  0.0003  oi" 
0.0002  mm.,  and  there  are  no  doubt  much  smaller  germs 
which  our  microscopes  fail  to  disclose. 

This  assumption  is  undoubtedly  correct. 

We  will,  in  the  first  instance,  make  a  rough  calculation 
of  what  would  happen  if  such  an  organism  were  detached 
from  the  earth  and  pushed  out  into  space  by  the  radiation 
pressure  of  our  sun.  The  organism  would  first  of  all  have 
to  cross  the  orbit  of  Mars;  then  the  orbits  of  the  smaller 
and  of  the  outer  planets.  .  .  .  The  organisms  would  cross 
the  orbit  of  Mars  after  twenty  days,  the  Jupiter  orbit  after 
eighty  days,  and  the  orbit  of  Neptune  after  fourteen  months. 
Our  nearest  solar  system  would  be  reached  in  nine  thousand 
years. 

For  the  assumption  of  eternity  of  life  only  the  transfer- 
ence of  germs  from  one  solar  system  to  another  would 
have  to  be  considered  and  the  question  arises  whether 
or  not  germs  can  keep  their  vitality  so  many  thousands 
of  years.  Arrhenius  thinks  that  this  is  possible  on 
account  of  the  low  temperature  (which  must  be  below 
—220°  C.)  at  which  no  chemical  reaction  and  hence 
no  decomposition  and  deterioration  are  possible  in  the 
spores ;  and  on  account  of  the  absence  of  water  vapour. 
The  question  then  arises :  Have  we  any  facts  to  war- 
rant the  assumption  that  spores  may  remain  alive  for 
thousands  of  years  under  such  conditions  and  retain 
their  power  of  germination?  We  know  that  seeds 
have  a  very  limited  vitality,  and  the  statement  that 


36  Living  and  Dead  Matter  and 

grain  found  in  the  Egyptian  tombs  was  still  able  to 
germinate  has  long  been  recognized  as  a  myth.  Miss 
White'  found  that  in  wheat  grains,  there  appeared  a 
well-marked  drop  in  their  germinating  power  after 
about  the  fourth  year,  reaching  zero  in  eleven  to  seven- 
teen years.  In  a  drier  climate  they  last  longer  than 
in  a  moist  climate.  It  is  of  importance  that  the  hydro- 
lyzing  enzymes  in  the  seeds,  such  as  diastase,  erepsin, 
remained  unimpaired  even  after  the  germinating  power 
of  the  seeds  had  disappeared.  The  seeds  were  able  to 
resist  for  two  days  the  temperature  of  liquid  air,  though 
the  subsequent  germination  was  delayed  by  this  treat- 
ment. Macfadyen^  exposed  non-sporing  bacteria,  viz., 
B.  typhosus,  B.  coli  communis,  Staphylococcus  pyogenes 
aureus,  and  a  Saccharomyces  to  liquid  air. 

The  experiments  showed  that  a  prolonged  exposure  of 
six  months  to  a  temperature  of  about  —  190°  has  no  ap- 
preciable effect  on  the  vitality  of  micro-organisms.  To  judge 
by  the  results  there  appeared  no  reason  to  doubt  that  the 
experiment  might  have  been  successfully  prolonged  for  a 
still  longer  period. 

Paul  BecquereP  found  that  seeds  which  possess  a  very 
thick  integument  may  live  longer  than  the  grain  in 
Miss  White's  experiments.  The  thickness  of  the  in- 
tegument prevents  the  exchange  of  gases  between  air 

*  White,  J.,  Proc.  Roy.  Soc,  1909,  B,  Ixxxi.,  417. 
"Macfadyen,  A.,  Proc.  Roy.  Soc,  1903,  Ixxi.,  76. 
3  Becquerel,  P.,  Revue  generate  des  Sciences,  1914,  xxv.,  559. 


The  Origin  of  Life  37 

and  seed.  Thus  seeds  of  leguminoses  {Cassia  hicapsu- 
laris,  Cytisus  biflorus,  LeuccEna  leucocephala,  and  Tri- 
folium  arvense)  had  retained  their  power  of  germination 
for  eighty-seven  years.  Becquerel  has  shown  that  the 
dryness  of  the  membrane  is  very  essential  for  such  a 
duration  of  Hfe,  since  when  dry  it  is  impermeable  for 
gases  and  the  slow  chemical  reactions  inside  the  grain 
become  impossible. 

In  the  cosmic  space  there  is  no  water  vapour,  no 
atmosphere,  and  a  low  temperature,  and  there  is  hence 
no  reason  why  spores  should  lose  appreciably  more  of 
their  germinating  power  in  ten  thousand  years  than  in 
six  months.  We  must  therefore  admit  the  possibility 
that  spores  may  move  for  an  almost  infinite  length 
of  time  through  cosmic  space  and  yet  be  ready  for  ger- 
mination when  they  fall  upon  a  planet  in  which  all 
the  conditions  for  germination  and  development  exist, 
e.  g.,  water,  proper  temperature,  and  the  right  nutritive 
substances  dissolved  in  the  water  (inclusive  of  free 
oxygen). 

While  thus  everything  is  favourable  to  Arrhenius's 
hypothesis,  Becquerel  raises  the  objection  that  the 
spores  going  through  space  would  yet  be  destroyed  by 
ultraviolet  light.  This  danger  would  probably  exist 
only  as  long  as  the  germ  is  not  too  far  from  a  sun.  The 
difficulty  is  a  real  one  since  the  ultraviolet  rays  have 
a  destructive  effect  even  in  the  absence  of  oxygen.  It 
is  possible,  however,  that  there  are  spores  which  can 


38  Living  and  Dead  Matter  and 

resist  this  effect  of  ultraviolet  light.  Arrhenius's 
theory  can  not  of  course  be  disproved  and  we  must 
agree  with  him  that  it  is  consistent  not  only  with  the 
theories  of  cosmogony  but  also  with  the  seeming  poten- 
tial immortality  of  certain  or  of  all  cells. 

The  alternative  to  Arrhenius's  theory  is  that  living 
matter  did  originate  and  still  originates  from  non-living 
matter.  If  this  idea  is  correct  it  should  one  day  be 
possible  to  discover  synthetic  enzymes  which  are  cap- 
able of  forming  molecules  of  their  own  kind  from  a 
simple  nutritive  solution.  With  such  synthetic  en- 
zymes as  a  starting  point  the  task  might  be  undertaken 
of  creating  cells  capable  of  growth  and  cell  division, 
at  least  in  the  apparently  simple  form  in  which  these 
phenomena  occur  in  bacteria;  viz.,  that  after  the  mass 
has  reached  a  certain  (still  microscopic)  size  it  divides 
into  two  cells  and  so  on.  If  Arrhenius  is  right  that 
living  matter  has  had  no  more  beginning  than  matter 
in  general,  this  hope  of  making  living  matter  artificially 
appears  at  present  as  futile  as  the  hope  of  making 
molecules  out  of  electrons. 

The  problem  of  making  living  matter  artificially 
has  been  compared  to  that  of  constructing  a  perpetuum 
mobile;  this  comparison  is,  however,  not  correct.  The 
idea  of  a  perpetuum  mobile  contradicts  the  first  law  of 
thermodynamics,  while  the  making  of  living  matter 
may  be  impossible  though  contradicting  no  natural  law. 

Pasteur's  proof  that   spontaneous  generation   does 


The  Origin  of  Life  39 


not  occur  in  the  solutions  used  by  him  does  not  prove 
that  a  synthesis  of  living  from  dead  matter  is  impossible 
under  any  conditions.  It  is  at  least  not  inconceivable 
that  in  an  earlier  period  of  the  earth's  history  radio- 
activity, electrical  discharges,  and  possibly  also  the 
action  of  volcanoes  might  have  furnished  the  combina- 
tion of  circumstances  under  which  living  matter  might 
have  been  formed.  The  staggering  difficulties  in 
imagining  such  a  possibility  are  not  merely  on  the 
chemical  side — e.  g.,  the  production  of  proteins  from 
CO  2  and  N — but  also  on  the  physical  side  if  the  neces- 
sity of  a  definite  cell  structure  is  considered.  We  shall 
see  in  the  sixth  chapter  that  without  a  structure  in  the 
egg  to  begin  with,  no  formation  of  a  complicated  organ- 
ism is  imaginable;  and  while  a  bacterium  may  have  a 
simple  structure,  such  a  structure  as  it  possesses  is  as 
necessary  for  its  existence  as  are  its  enzymes. 

Attempts  have  repeatedly  been  made  to  imitate  the 
structiires  in  the  cell  and  of  living  organisms  by  colloidal 
precipitates.  It  is  needless  to  point  but  that  such 
precipitates  are  of  importance  only  for  the  study  of  the 
origin  of  structures  in  the  living,  but  that  they  are  not 
otherwise  an  imitation  of  the  living  since  they  are 
lacking  the  characteristic  synthetic  chemical  processes. 


/ 


CHAPTER  III 

THE  CHEMICAL  BASIS   OF   GENUS  AND   SPECIES 

'     I.     It  is  a  truism  that  from  an  egg  of  a  species  an 

organism  of  this  species  only  and  of  no  other  will  arise. 

It  is  also  a  truism  that  the  so-called  protoplasm  of  an 

egg    does    not    differ    much    from    that    of    eggs    of 

other  species  when  looked  at  through  a  microscope. 

The  question  arises:  What  determines  the  species  of 

the  future  organism?     Is  it  a  structure  or  a  specific 

chemical  or  groups  of  chemicals?      In  a  later  chapter 

we   shall   show   that   the   egg   has   a  simple   though 

definite   structure,  but  in    this  chapter  we  shall  see 

that   the  egg   must  contain  specific  substances   and 

that  these  substances  which  determine  the  "species" 

and  specificity  in  general  are  in  all  probability  proteins. 

Since  solutions  of  different  proteins  look  alike  under  a 

microscope  we  need  not  wonder  that  it  is  impossible 

to  discriminate  microscopically  between  the  protoplasm 

of  different  eggs. 

"^  The  idea  of  definiteness  and  constancy  of  species,  a 

matter  of  daily  observation  in  the  case  of  man  and 

40 


Chemical  Basis  of  Genus  and  Species    41 

higher  animals  in  general,  was  not  so  readily  accepted 
in  the  case  of  the  micro-organisms,  which  on  account 
of  their  minuteness  and  simplicity  of  structure  are  not 
so  easy  to  differentiate.  There  existed  for  a  long  time 
serious  doubt  whether  or  not  the  simplest  organisms, 
the  bacteria,  possessed  a  definite  "specificity"  like 
the  higher  organisms,  or  whether  they  were  not  en- 
dowed, as  Warming  put  it,  with  an  "unlimited  plasti- 
city," which  forbade  classifying  them  according  to 
their  form  into  definite  species  as  Cohn  had  done.  An 
interesting  episode  in  this  discussion,  which  was  settled 
about  twenty-five  years  ago  arose  concerning  the  sulphur 
bacteria,  which  often  develop  in  large  masses  on  parts 
of  decaying  plants  or  animals  along  the  shore.  Sir  E. 
Ray  Lankester  found  collections  of  red  bacteria  cover- 
ing putrefying  animal  matter  in  a  vessel  and  forming 
a  continuous  membrane  along  its  wall.  These  red 
bacteria  were  of  very  different  shape,  size,  and  group- 
ing, but  they  seemed  to  be  connected  by  transition  forms. 
They  had  a  common  character,  however,  namely,  their 
peach-coloured  appearance.  This  common  character, 
together  with  their  association  in  the  same  habitat, 
led  Lankester  to  the  then  justifiable  belief  that  they 
all  belonged  to  one  species  which  was  protean  in  char- 
acter and  that  the  different  forms  were  only  to  be 
considered  as  phases  of  growth  of  this  one  species. 
The  presence  of  the  same  red  pigment  "  Bacterio-pur- 
purin"    seemed   justly   to   indicate   the   existence   of 


42    Chemical  Basis  of  Genus  and  Species 

common  chemical  processes.  Cohn,  on  the  contrary, 
considered  the  different  forms  among  these  red  bacteria 
(they  are  today  called  sulphur  bacteria  since  they 
oxidize  the  hydrogen  sulphide  produced  by  bacteria 
of  putrefaction  to  sulphur  and  sulphates)  as  definite 
and  distinct  species,  in  spite  of  their  common  colour 
and  their  association.  Later  observations  showed  that 
Cohn  was  right.  Winogradsky '  succeeded  in  proving 
by  pure  culture  experiments  that  each  of  these  different 
forms  of  sulphur  bacteria  was  specific  and  did  not  give 
rise  to  any  of  the  other  forms  of  the  same  colour  found 
in  the  same  conditions. 

The  method  of  pure  line  breeding  inaugurated  by 
Johannsen^  has  shown  that  the  degree  of  definiteness 
goes  so  far  that  apparently  identical  forms  with  only 
slight  differences  in  size  may  breed  true  to  this  size; 
but  for  reasons  which  will  become  clear  later  on  we 
may  doubt  whether  they  are  to  be  considered  as  definite 
species. 

The  fact  of  specificity  is  supported  by  the  fact  of 
constancy  of  forms,  de  Vries  has  pointed  out  that 
regardless  of  the  possible  origin  of  new  species  by  muta- 
tion the  old  species  may  persevere.  Walcott  has  found 
fossils  of  annelids,  snails,  crustaceans,  and  algae  in  a 
precambrian  formation  in  British  Columbia  whose  age 

^  Winogradsky,  S.,  Beitrdge  zur  Morphologic  und  Physiologic  dcr 
Baclerien.     Leipzig,  1888. 

'  Johannsen,  W.,  Elemenle  dcr  exacten  Erblichkeitslehre.     2d  ed.,  1913. 


Chemical  Basis  of  Genus  and  Species    43 

(estimated  on  the  rate  of  formation  of  radium  from 
.uranium)  may  be  about  two  hundred  million  years  and 
estimated  on  the  basis  of  sedimentation  sixty  million 
years.  And  yet  these  invertebrates  are  so  closely 
related  to  the  forms  existing  today  that  the  systematists 
have  no  difficulty  in  finding  the  genus  among  the  modem 
forms  into  which  each  of  these  organisms  belongs.  W. 
M.  Wheeler,  in  his  investigations  of  the  ants  enclosed 
in  amber,  was  able  to  identify  some  of  them  with  forms 
living  today,  though  the  ants  observed  in  the  amber 
must  have  been  two  million  years  old.  The  constancy 
of  species,  i.  e.,  the  permanence  of  specificity  may  there- 
fore be  considered  as  established  as  far  back  as  two  or 
possibly  two  hundred  millions  of  years.  The  definite- 
ness  and  constancy  of  each  species  must  be  deter- 
mined by  something  equally  definite  and  constant  in 
the  egg,  since  in  the  latter  the  species  is  already  fixed 
irrevocably. 

We  shall  show  first  that  species  if  sufficiently  sepa- 
rated are  generally  incompatible  with  each  other  and 
that  any  attempt  at  fusing  or  mixing  them  by  grafting 
or  cross-fertilizing  is  futile.  In  the  second  part  of  the 
chapter  we  shall  take  up  the  facts  which  seem  destined 
to  give  a  direct  answer  to  the  question  as  to  the  cause 
of  specificity.  It  is  needless  to  say  that  this  latter 
question  is  of  paramount  importance  for  the  problem 
of  evolution,  as  well  as  for  that  of  the  constitution  of 
living  matter. 


44    Chemical  Basis  of  Genus  and  Species 

/.     The  Incompatibility  oj  Species  not  closely  Related 

2.  It  is  practically  impossible  to  transplant  organs 
or  tissues  from  one  species  of  higher  animals  to  an- 
other, unless  the  two  species  are  very  closely  related; 
and  even  then  the  transplantation  is  uncertain  and 
the  graft  may  either  fall  off  again  or  be  destroyed. 
This  specificity  of  tissues  goes  so  far  that  surgeons 
prefer,  when  a  transplantation  of  skin  in  the  human  is 
intended,  to  use  skin  of  the  patient  or  of  close  blood 
relations.  The  reason  why  the  tissues  of  a  foreign 
species  in  warm-blooded  animals  cannot  grow  well  on 
a  given  host  has  been  explained  by  the  remarkable 
experiments  of  James  B.  Murphy  of  the  Rockefeller 
Institute.^  Murphy  discovered  that  it  is  possible  to 
transplant  successfully  any  kind  of  foreign  tissue  upon 
the  early  embryo  of  the  chick.  Even  human  tissue 
transplanted  upon  the  chick  embryo  will  grow  rapidly. 
This  shows  that  at  this  early  stage  the  chick  embryo 
does  not  yet  react  against  foreign  tissue.  This  lack 
of  reaction  lasts  until  about  the  twenty-first  day  in 
the  life  of  the  embryo ;  then  the  growth  of  the  graft  not 
only  ceases  but  the  graft  itself  falls  off  or  is  destroyed. 
Murphy  noticed  that  this  critical  period  coincides  with 
the  development  of  the  spleen  and  of  lymphatic  tissue 
in  the  chick  and  that  a  certain  type  of  migrating  cells, 

'  Murphy,  J.  B.,  Jour.  Exper.  Med.,  1913,  xvii.,  482;  1914,  xix.,  181; 
six.,  513;  Murphy  and  Morton,  J.  J.,  Jour.  Exper.  Med.,  1915,  xxii.,  204. 


Chemical  Basis  of  Genus  and  Species    45 

the  so-called  lymphocytes,  which  develop  in  the  lym- 
phatic tissue,  gather  at  the  edge  of  the  graft  in  great 
numbers,  and  he  suggested  that  these  lymphocytes  (by 
a  secretion  of  some  substance?)  rid  the  host  of  the 
graft.  He  applied  two  tests  both  of  which  confirmed 
this  idea.  First  he  showed  that  when  small  fragments  of 
the  spleen  of  an  adult  chicken  are  transplanted  into  the 
embryo  the  latter  loses  its  tolerance  for  foreign  grafts. 
The  second  proof  is  still  more  interesting.  It  was  known 
that  by  treatment  with  Roentgen  rays  the  lymphocytes 
in  an  animal  could  be  destroyed.  It  was  to  be  expected 
that  an  animal  so  treated  would  have  lost  its  specific 
resistance  to  foreign  tissues.  Murphy  found  that  this 
was  actually  the  case.  On  fully  grown  rats  in  which 
the  lymphocytes  had  been  destroyed  by  X-rays  (as 
ascertained  by  blood  counts)  tissues  of  foreign  species 
grew  perfectly  well.  These  experiments  have  assumed 
a  great  practical  importance  since  they  can  also  be 
applied  to  the  immunization  of  an  animal  against 
transplanted  cancer  of  its  own  species.  Murphy  found 
that  by  increasing  the  number  of  lymphocytes  in  an 
animal  (which  can  be  accomplished  by  a  mild  treatment 
with  X-rays)  the  immunity  against  foreign  grafts  as 
well  as  against  cancer  from  the  same  species  can  be 
increased.  It  is  quite  possible  that  the  apparent  im- 
munity to  a  transplantation  of  cancer  produced  by 
Jensen,  Leo  Loeb,  and  Ehrlich  and  Apolant  through 
the  previous  transplantation  of  tissue  in  such  an  animal 


46    Chemical  Basis  of  Genus  and  Species 

was  due  to  the  fact  that  this  previous  tissue  transplan- 
tation led  to  an  increase  in  the  number  of  lymphocytes 
in  the  animal.  The  medical  side,  however,  lies  outside 
of  our  discussion,  and  we  must  satisfy  ourselves  with 
only  a  passing  notice.  The  facts  show  that  each  warm- 
blooded animal  seems  to  possess  a  specificity  whereby 
its  lymphocytes  destroy  transplanted  tissue  taken 
from  a  foreign  species. 

A  lesser  though  still  marked  degree  of  incompatibility 
exists  also  in  lower  animals  for  grafts  from  a  different 
species,^  The  graft  may  apparently  take  hold,  but 
only  for  a  few  days,  if  the  species  are  not  closely 
related.  Joest  apparently  succeeded  in  making  a  per- 
manent union  between  the  anterior  and  posterior  ends 
of  two  species  of  earthworms,  Lumhricus  rubellus  and 
Allolobophora  terrestris.  Born  and  later  Harrison 
healed  pieces  of  tadpoles  of  different  species  together. 
An  individual  made  up  of  two  species  Rana  virescens 
and  Rana  palustris  lived  a  considerable  time  and  went 
through  metamorphosis.  Each  half  regained  the  char- 
acteristic features  of  the  species  to  which  it  belonged. 
It  seems,  however,  that  if  species  of  tadpoles  of  two 
more  distant  species  are  grafted  upon  each  other  no 
lasting  graft  can  be  obtained,  e.  g.,  Rana  esculenta  and 
Bombinator  igneus.  These  experiments  were  made  at 
a  time  when  the  nature  and  bearing  of  the  problem  of 

'  The  reader  is  referred  to  Morgan's  book  on  Regeneration  (New 
York,  1901),  for  the  literature  on  this  subject. 


Chemical  Basis  of  Genus  and  Species    47 

specificity  was  not  yet  fully  recognized.  The  r61e  of 
lymphocytes  in  these  cases  has  never  been  investigated. 
The  grafted  piece  always  retained  the  characteristics 
of  the  species  from  which  it  was  taken. 

Plants  possess  no  leucocytes  and  we  therefore  see 
that  they  tolerate  a  graft  of  foreign  tissues  better  than 
is  the  case  in  animals.  As  a  matter  of  fact  heteroplastic 
grafting  is  a  common  practice  in  horticulture,  although 
even  here  it  is  known  that  indiscriminate  heteroplastic 
grafting  is  not  feasible  and  that_.therefore  the  specificity 
is  not  without  influence*  'The  host  is  supposed  to  fur- 
nish only  nutritive  sap  to  the  graft  and  in  this  respect 
does  not  behave  very  differently  from  an  artificial  nutri- 
tive solution  for  the  raising  of  a  plant.  The  law  of 
specificity,  however,  remains  true  also  for  the  grafted 
tissues :  neither  in  animals  nor  in  plants  does  the  graft 
lose  its  specificity,  and  it  never  assumes  the  specific 
characters  of  the  host,  or  vice  versa.  The  apparent 
exceptions  which  Winkler  believed  he  had  foimd  in  the 
case  of  grafts  of  nightshade  on  tomatoes  turned  out  to 
be  a  further  proof  of  the  law  of  specificity.  Winkler, 
after  the  graft  had  taken,  cut  through  the  place  of 
grafting,  after  which  operation  a  callus  formation  oc- 
curred on  the  wound.  In  most  cases  either  a  pure 
nightshade  or  a  pure  tomato  grew  out  from  this  callus. 
In  some  cases  he  obtained  shoots  from  the  place 
where  graft  and  host  had  united,  which  on  one  side 
were  tomato,   on  the  other  side  nightshade.     What 


4S    Chemical  Basis  of  Genus  and  Species 

really  happened  was  that  the  shoots  had  a  growing 
point  whose  cells  on  the  one  side  consisted  of  cells  of 
nightshade,  on  the  other  side  of  tomato.  ^  We  know  of 
no  case  in  which  the  cell  of  a  graft  has  lost  its  specificity 
and  undergone  a  transformation  into  the  cell  of  the  host. 
3.  Another  manifestation  of  the  incompatibility 
of  distant  species  is  found  in  the  domain  of  fertiliza- 
tion. The  eggs  of  the  majority  of  animals  cannot 
develop  unless  a  spermatozoon  enters.  The  entrance 
of  a  spermatozoon  into  an  egg  seems  also  to  fall  under 
the  law  of  specificity,  inasmuch  as  in  general  only  the 
sperm  of  the  same  or  a  closely  related  species  is  able 
to  enter  the  egg.  The  writer^  has  found,  however,  that 
it  is  possible  to  overcome  the  limitation  of  specificity 
in  certain  cases  by  physicochemical  means,  and  by  the 
knowledge  of  these  means  we  may  perhaps  one  day  be 
able  to  more  closely  define  the  mechanism  of  specificity 
in  this  case.  He  found  that  the  eggs  of  a  certain  Cali- 
fornian  sea  urchin,  which  cannot  be  fertilized  by  the 
sperm  of  starfish  in  normal  sea  water,  will  lose  their 
specificity  towards  this  type  of  foreign  sperm  if  the 
sea  water  is  rendered  a  little  more  alkaline,  or  if  a  little 
more  Ca  is  added  to  the  sea  water,  or  if  both  these 
variations  are  effected.  Godlewski  has  confirmed  the 
efficiency  of  this  method  for  the  fertilization  of  sea- 
urchin  eggs  with  the  sperm  of  crinoids. 

'  Baur,  E.,  Einfiihrung  in  die  experimentelle  Vererbungslehre.     Berlin, 
1911,  p.  232. 

'  Literature  on  this  subject  in  Chapter  IV. 


Chemical  Basis  of  Genus  and  Species    49 

If  such  heterogeneous  hybridizations  are  carried  out, 
two  striking  results  are  obtained.     The  one  is  that 


Fig.  I.  Five-days-old  larvs  from  a  sea  urchin  (Strongy- 
locentrotus  purpuratus)  9  and  a  starfish  (Asterias)  cT. 
(Front  view.) 

the  resulting  larva  has  only  maternal  characteristics 
(Figs.  I  and  2) ,  as  if  the  sperm  had  contributed  no  he- 


FiG,  2.  Five-days-old  larvas  of  Strongylocentrotus  purpur- 
atus produced  by  artificial  parthenogenesis.  (Side  view.) 
The  larvae  in  Figs,  i  and  2  are  identical  in  appearance, 
proving  that  heterogeneous  hybridization  leads  to  a  larva 
with  purely  maternal  characters. 


it 


reditary  material  to  the  developing  embryo. /This  result 
could  not  have  been  predicted,  for  if  we  fertilize  the 
egg  of  the  same  Calif ornian  sea  urchin,  Strongylocen- 
trotus purpuratus,  with  the  sperm  of  a  very  closely 


50    Chemical  Basis  of  Genus  and  Species 

related  sea  urchin,  S.  franciscanus,  the  hereditary 
effect  of  the  spermatozoon  is  seen  very  distinctly  in  the 
primitive  skeleton  formed  by  the  larva.'  (Fig.  3.) 
In  the  case  of  the  heterogeneous  hybridization  the 
spermatozoon  acts  practically  only  as  an-  activating 
agency  upon  the  egg  and  not  as  a  transmitter  of  paternal 
qualities. 

The  second  striking  fact  is  that  while  the  sea-urchin 


Fig.  3.  Five-days-old  larvae  of  two  closely  related  forms  of  sea 
urchins  (S.  purpura tus  9  and  S.  franciscanus  cf).  In  this 
case  the  larva  has  also  paternal  characters  as  shown  by  the 
skeleton. 

eggs  fertilized  with  starfish  sperm  develop  at  first 
perfectly  normally  they  begin  to  die  in  large  numbers 
on  the  second  and  third  day  of  their  development,  and 
only  a  very  small  number  live  long  enough  to  form  a 
skeleton;  and  these  are  usually  sickly  and  form  the 
skeleton  considerably  later  than  the  pure  breed.  It  is 
not  quite  certain  whether  the  sickliness  of  these  hetero- 
geneous hybrids  begins  or  assumes  a  severe  character 

'  Loeb,  J.,  King,  W.  O.  R.,  and  Moore,  A.  R.,  Arch.  f.  Entwicklngs- 
mech.,  19 10,  xxix.,  354. 


Chemical  Basis  of  Genus  and  Species    51 

with  the  development  of  a  certain  type  of  wandering 
cells,  the  mesenchyme  cells;  it  would  perhaps  be  worth 
while  to  investigate  this  possibility.  The  writer  was 
under  the  impression  that  this  sickliness  might  have 
been  brought  about  by  a  poison  gradually  formed  in 
the  heterogeneous  larvae. 

He  investigated  the  effects  of  heterogeneous  hybridi- 
zation also  in  fishes,  which  are  a  much  more  favourable 
object.  The  egg  of  the  marine  fish  Fundulus  hetero- 
clitus  can  be  fertilized  with  the  sperm  of  almost  any 
other  teleost  fish,  as  Moenkhaus'  first  observed. 
This  author  did  not  succeed  in  keeping  the  hybrids 
alive  more  than  a  day,  but  the  writer  has  kept  many 
heterogeneous  hybrids  alive  for  a  month  or  longer,^ 
and  found  the  same  two  striking  facts  which  he  had 
already  observed  in  the  heterogeneous  cross  between 
sea  urchin  and  starfish:  first,  practically  no  transmis- 
sion of  paternal  characters,  and  second,  a  sickly  con- 
dition of  the  embryo  which  begins  early  and  which 
increases  with  further  development.  The  heterogene- 
ous fish  hybrids  between,  e.  g.,  Fundulus  heteroclitus  9 
and  Menidia  d^  have  usually  no  circulation  of  blood, 
although  the  heart  is  formed  and  beats  and  blood- 
vessels and  blood  cells  are  formed;  the  eyes  are  often 
incomplete  or  abnormal  though  they  may  be  normal 
at  first ;  the  growth  of  the  embryo  is  mostly  retarded. 

^  Moenkhaus,  W.  J.,  Am.  Jour.  Anat.,  1904,  iii.,  29. 
"Loeb,  J.,  Jour.  Morphol.,  1912,  xxiii.,  i. 


52    Chemical  Basis  of  Genus  and  Species 

In  exceptional  cases  circulation  may  be  established 
and  in  these  a  normal  embryo  may  result,  but  such  an 
embryo  is  chiefly  maternal. 

This  incompatibility  of  two  gametes  from  different 
species  does  not  show  itself  in  the  case  of  heterogeneous 
hybridization  only,  but  also  though  less  often  in  the 
case  of  crossing  between  two  more  closely  related 
forms.  The  cross  between  the  two  related  forms  S. 
purpuratus  9  and  S.  franciscanus  cf  is  very  sturdy  and 
shows  no  abnormal  mortality  as  far  as  the  writer's  ob- 
servations go.  If,  however,  the  reciprocal  crossing  is 
carried  out,  namely  that  of  S.  franciscanus  9  and  S. 
purpuratus  cf ,  the  development  is  at  first  normal,  but 
beginning  with  the  time  of  mesenchyme  formation 
the  majority  of  larvae  become  sickly  and  die ;  and  again 
the  question  may  be  raised  whether  or  not  the  begin- 
ning of  sickliness  coincides  with  the  development  of 
mesenchyme  cells.  If  we  assume  that  the  sickliness 
and  death  are  due  to  the  formation  of  a  poison,  we 
must  assume  that  the  poison  is  formed  by  the  proto- 
plasm of  the  egg,  since  otherwise  we  could  not  under- 
stand why  the  reciprocal  cross  should  be  healthy. 

All  of  these  data  agree  in  this  one  point,  that  the 
fusion  by  grafting  or  fertilization  of  two  distant  species 
is  impossible,  although  the  mechanism  of  the  incompat- 
ibility is  not  yet  understood.  It  is  quite  possible  that 
this  mechanism  is  not  the  same  in  all  the  cases  men- 
tioned here,  and  that  it  may  be  different  when  two 


Chemical  Basis  of  Genus  and  Species    53 

different  species  are  mixed  and  when  incompatibility 
exists  between  varieties,  as  is  the  case  in  the  graft  on 
mammals. 

//.     The  Chemical  Basis  of  Genus  and  Species  and  of 

Species  Specificity 

4.  Fifty  or  sixty  years  ago  surgeons  did  not  hesitate 
to  transfuse  the  blood  of  animals  into  human  beings. 
The  practice  was  a  failure,  and  Landois^  showed  by 
experiment  that  if  blood  of  a  foreign  species  was  intro- 
duced into  an  animal  the  blood  corpuscles  of  the  trans- 
fused blood  were  rapidly  dissolved  and  the  animal  into 
which  the  transfusion  was  made  was  rendered  ill  and 
often  died.  The  result  was  different  when  the  animals 
whose  blood  was  used  for  the  purpose  of  transfusion 
belonged  to  the  same  species  or  a  species  closely  related 
to  the  animal  into  which  the  blood  was  transfused. 
Thus  when  blood  was  exchanged  between  horse  and 
donkey  or  between  wolf  and  dog  or  between  hare  and 
rabbit  no  hemoglobin  appeared  in  the  urine  and  the 
animal  into  which  the  blood  was  transfused  remained 
well.^  This  was  the  beginning  of  the  investigations 
in  the  field  of  serum  specificity  which  were  destined  to 
play  such  a  prominent  role  in  the  development  of  medi- 
cine.    Friedenthal  was  able  to  show  later  that  if  to 

^  Landois,  L.,  Zur  Lehre  von  der  Bluttransfusion.     Leipzig,  1875. 
'  This  is  probably  true  only  within  the  limits  of  exactness  used  in 
these  experiments. 


54    Chemical  Basis  of  Genus  and  Species 

10  c.c.  of  serum  of  a  mammal  three  drops  of  defibrinated 
blood  of  a  foreign  species  are  added  and  the  whole  is 
exposed  in  a  test  tube  to  a  temperature  of  38°C.  for 
fifteen  minutes  the  blood  cells  contained  in  the  added 
blood  are  all  cytolyzed;  that  this,  however,  does  not 
occur  so  rapidly  when  the  blood  of  a  related  species  is 
used.  He  could  thus  show  that  human  blood  serum 
dissolves  the  erythrocytes  of  the  eel,  the  frog,  pigeon, 
hen,  horse,  cat,  and  even  that  of  the  lower  monkeys 
but  not  that  of  the  anthropoid  apes.  The  blood  of  the 
chimpanzee  and  of  the  human  are  no  longer  incom- 
patible, and  this  discovery  was  justly  considered  by 
Friedenthal  as  a  confirmation  of  the  idea  of  the  evolu- 
tionists that  the  anthropoid  apes  and  the  human  are 
blood  relations.  ^ 

This  line  of  investigation  had  in  the  meanwhile 
entered  upon  a  new  stage  when  Kraus,  Tchistowitch, 
and  Bordet  discovered  and  developed  the  precipitin  re- 
action, which  consists  in  the  fact  that  if  a  foreign  serum 
(or  a  foreign  protein)  is  introduced  into  an  animal  the 
blood  serum  of  the  latter  acquired  after  some  time 
the  power  of  causing  a  precipitate  when  mixed  with 
the  antigen,  i.  e.,  with  the  foreign  substance  originally 
introduced  into  the  animal  for  the  purpose  of  causing 
the  production  of  antibodies  in  the  latter;  while,  of 
course,  no  such  precipitation  occurs  if  the  serum  of  a 

'Friedenthal,  H.,  " Experimenteller  Nachweis  der  Blutverwandt- 
schaft."     Arch.  J.  Physiol.,  1900,  494. 


Chemical  Basis  of  Genus  and  Species    55 

non-treated  rabbit  is  mixed  with  the  serum  of  the  blood 
of  the  foreign  species. 

In  1897  Kraus  discovered  that  if  the  filtrates  from 
cultures  of  bacteria  {e.  g.,  typhoid  bacillus)  are  mixed 
with  the  serum  of  an  animal  immunized  with  the  same 
serum  {e.  g.,  typhoid  serum)  it  causes  a  precipitate;  and 
that  this  precipitin  reaction  is  specific.  This  fact 
was  confirmed  and  has  been  extended  by  the  work 
of  many  authors. 

Tchistowitch  in  1899  observed  that  the  serum  of 
rabbits  which  had  received  injections  of  horse  or  eel 
serum  caused  a  precipitate  when  mixed  with  the  serum 
of  these  latter  animals. 

Bordet  found  in  1899  that  if  milk  is  injected  into  a 
rabbit  the  serum  of  such  a  rabbit  acquires  the  power 
of  precipitating  casein,  and  Fish  found  that  this  reac- 
tion is  specific  inasmuch  as  the  lactoserum  from  cow's 
milk  can  precipitate  only  the  casein  of  cow's  milk  but 
not  that  of  human  or  goat  milk.  Wassermann  and 
Schutze  reached  the  same  result  independently  of  each 
other. 

Myers  and  later  Uhlenhuth  showed  that  if  white  of 
egg  from  a  hen's  egg  is  injected  into  a  rabbit,  precipitins 
for  white  of  egg  are  found  in  the  serum  of  the  latter, 
and  Uhlenhuth^  found,  by  trying  the  white  of  egg  of 
different  species  of  birds,  that  the  precipitin  reaction 

'  Uhlenhuth,  P.,  and  Steffenhagen,  K.,  Kolle-Wassermann,  Handh. 
d.  pathol.  Mikroorg.,  2nd  Ed.,  1913,  iii.,  257. 


56    Chemical  Basis  of  Genus  and  Species 

called  forth  by  the  blood  of  the  immunized  animal  is 
specific,  inasmuch  as  the  proteins  from  a  hen's  egg 
will  call  forth  the  formation  of  precipitins  in  the  blood 
of  the  rabbit  which  will  precipitate  only  the  white  of 
egg  of  the  hen  or  of  closely  related  birds. 

To  Nuttall '  belongs  the  credit  of  having  worked  out 
a  quantitative  method  for  measuring  the  amount  of 
precipitate  formed,  and  in  this  way  he  made  it  possible 
to  draw  more  valid  conclusions  concerning  the  degree 
of  specificity  of  the  precipitin  reaction.  He  found 
by  this  method  that  when  the  immune  serum  is 
mixed  with  the  serum  or  the  protein  solution  used  for 
the  immunization  a  maximum  precipitate  is  formed, 
but  if  it  is  mixed  with  the  serum  of  related  forms  a 
quantitatively  smaller  precipitate  is  produced.  In 
this  way  the  degree  of  blood  relationship  could  be 
ascertained.  He  thus  was  able  to  show  that  when  the 
blood  of  one  species,  e.  g.,  the  human,  was  injected  into 
the  blood  of  a  rabbit,  after  some  time  the  serum  of  the 
rabbit  was  able  to  cause  a  precipitate  not  only  with  the 
serum  of  man,  or  chimpanzee,  but  also  of  some  lower 
monkeys;  with  this  difference,  however,  that  the  pre- 
cipitate was  much  heavier  when  the  immune  serum  was 
added  to  the  serum  of  man.  The  method  thus  shows 
the  existence  of  not  an  absolute  but  of  a  strong  quanti- 
tative specificity  of  blood  serum.     This  statement  may 

'  Nuttall,  George  H.  F.,  Blood  Immunity  and  Blood  Relationship, 
Cambridge  Univ.  Press,  1904. 


Chemical  Basis  of  Genus  and  Species    57 

be  illustrated  by  the  following  table  from  Nuttall. 
The  antiserum  used  for  the  precipitin  reaction  was 
obtained  by  treating  a  rabbit  with  human  blood  serum. 
The  forty-five  bloods  tested  had  been  preserved  for 
various  lengths  of  time  in  the  refrigerator  with  the 
addition  of  a  small  amount  of  chloroform. 

TABLE  II 

Quantitative  Tests  with  Anti-Primate  Sera 

Tests  with  Ayitihuman  Serum 


Blood  of 

Precipitum 
Amount 

Percentage 

Primates 

Man 

.031 

.04 

.021 

•013 
.013 
.009 
.009 

.0 

.003 

.001 

.003 

.0025 

.001 

,001 

.0008 

.0005 

•003 

.003 

.002 

.002 

.002 

.0005 

.0005 

.0 

100 

Chimpanzee 

130  (loose  precipitum) 

Gorilla 

64 

Ourang 

42 

Cynocephalus  mormon 

Cynocephalus  sphinx 

Ateles  geoffroyi 

42 
29 
29 

Insedivora 

Centetes  ecaudatus 

0 

Carnivora 

Canis  aureus 

10  (loose  precipitum) 

Canis  famiharis 

3 

Lutra  vulgaris 

10  (concentrated  serum) 

XJrsus  tibetanus 

8 

Genetta  tigrina 

3 

Felis  domesticus 

3 

Felis  caracal 

3 

Felis  tigris 

2 

Ungulata 
Ox 

ID 

Sheep    

10 

Cobus  unctuosus 

7 

Cervus  porcinus 

7 

Rangifer  tarandus 

7 

Capra  negaceros 

2 

Equus  caballus 

2 

Sus  scrofa 

0 

58    Chemical  Basis  of  Genus  and  Species 


Blood  of 

Precipitum 
Amount 

Percentage 

Rodentia 

Dasyprocta  cristata 

Guinea-pig 

.002 

.0 
.0 

.o 

7  (concentrated    serum 
clots) 

0 

Rabbit            

0 

Marsupialia 

Petrogale  xanthopus ' 

Petrogale  penicillata 

Onychogale  frenata 

Onychogale  unguifera • 

Onychogale  unguifera 

Macropus  bennetti 

Thylacinus  cynocephalus. . 

0 

Among  the  Primate  bloods  that  of  the  Chimpanzee 
gave  too  high  a  figure,  owing  to  the  precipitum  being  floc- 
culent  and  not  settling  well,  for  some  reason  which  could 
not  be  determined.  The  figure  given  by  the  Ourang  is 
somewhat  too  low,  and  the  difference  between  Cynocepha- 
lus sphinx  and  Ateles  is  not  as  marked  as  might  have 
been  expected  in  view  of  the  qualitative  tests  and  the  series 
following.  The  possibilities  of  error  must  be  taken  into 
account  in  judging  of  these  figures;  repeated  tests  should  be 
made  to  obtain  something  like  a  constant.  Other  bloods 
than  those  of  Primates  give  small  reactions  or  no  reactions 
at  all.  The  high  figures  (io%)  obtained  with  two  Car- 
nivore bloods  can  be  explained  by  the  fact  that  one  gave 
a  loose  precipitum,  and  the  other  was  a  somewhat  concen- 
trated serum.  ^ 


We  have  mentioned  that  even  the  proteins  of  the 
egg  are  specific  according  to  Uhlenhuth.  Graham 
Smith,  one  of  Nuttall's  collaborators,  applied  the  lat- 

'  Nuttall,  Blood  Imfnunity  and  Blood  Relationship,  pp.  319  and  320. 


Chemical  Basis  of  Genus  and  Species    59 


ter's  quantitative  method  to  this  problem  and  confirmed 
the  results  of  Nuttall.  A  few  examples  may  serve  as 
an  illustration. 

TABLE  III 
Tests  with  Anti-Duck's-Egg  Serum 


Material  tested 

Amount  of 
precipitum 

Percentage 

Duck's                    egg-al 

Dumin 

.0384 
.0328 
.0234 
.0140 
.0065 
.0051 
.0046 
.0046 
.0018 
trace 

trace 

100 

85 

Fowl's                              ' 

61 

Silver  Pheasant's            ' 

36 

Blackbird's                      ' 

15 

Crane's                            ' 

14 

Moorhen's                       ' 

12 

Thrush's                          ' 

12 

Emu's 

5 

Hedge-Sparrow's            ' 

Chaffinch's                      * 

? 

0 

Tortoise  serum 
Turtle  serum 
Alligator  serum 

? 

? 

0 

Frog,  Amphiuma,  and  Dogfish  sera,  as  well  as  Tortoise  and 
Dogfish  egg-albumins,  were  also  tested,  with  negative  results. 

TABLE  IV 
Tests  with  Anti-Fowl's-Egg  Serum 


Material  tested 


Fowl's 

Fowl's 

Silver  Pheasant's 

Pheasant's 

Crane's 

Blackbird's 

Duck's 

Moorhen's 


egg-albumin  (old) . . 
(fresh). 


Amount  of 
precipitum 


.0159 
.0140 
.0075 
.0075 
.0046 
.0046 
.0037 
.0028 


Percentage 


47 
47 
29 
29 

23 

18 


6o    Chemical  Basis  of  Genus  and  Species 

Thrush,  Emu,  Greenfinch,  and  Hedge-sparrow  egg-albu- 
mins were  tested  and  gave  traces  of  precipita,  as  also  did 
Tortoise  and  Turtle  sera.  The  egg-albumins  of  the  Tor- 
toise, Frog,  Skate,  and  two  species  of  Dogfish  did  not  react. 
Alligator,  Frog,  Amphiuma,  and  Dogfish  sera  also  yielded 
no  results.^ 

By  improving  the  quantitative  method  in  various 
ways,  Welsh  and  Chapman^  were  able  to  explain  why 
the  precipitin  reaction  with  egg-white  was  not  strictly 
specific  but  gave  also,  though  quantitatively  weaker, 
results  with  the  egg-white  of  related  birds.  They 
found  that  by  a  new  method  devised  by  them  "it  is 
possible  to  indicate  in  an  avian  egg-white  antiserum 
the  presence  of  a  general  avian  antisubstance  (pre- 
cipitin) together  with  the  specific  antisubstance." 

The  Bordet  reaction  was  not  only  useful  in  indicating 
the  specificity  and  blood  relationship  for  animals  but 
also  among  plants.  Thus  Magnus  and  Friedenthal^ 
were  able  to  demonstrate  with  Bordet 's  method  the 
relationship  between  yeast  (Saccharomyces  cerevisice) 
and  truffle  (Tuber  hrumale). 

5.  We  must  not  forget,  while  under  the  spell  of 
the  problem  of  immunity,  that  we  are  interested  at 
the  moment  in  the  question  of  the  nature  of  the  speci- 
ficity of  living  organisms.     It  is  only  logical  to  conclude 

^  Nuttall,  pp.  345  and  346. 

'Welsh,  D.  A.,  and  Chapman,  H.  G.,  Jour.  Hygiene,  1910,  x.,  177. 
3  Magnus,  W.,  and  Friedenthal,  H.,  Ber.  d.  deutsch.  hot.  Cesellsch., 
1906,  xxiv.,  601. 


Chemical  Basis  of  Genus  and  Species    6i 

that  the  fossil  forms  of  invertebrate  animals  and  of  algae 
and  bacteria,  which  Walcott  found  in  the  Cambrian  and 
which  may  be  two  hundred  milHon  years  old,  must 
have  had  the  same  specificity  at  that  time  as  they  or 
their  close  relatives  have  today;  and  this  raises  the 
question:  What  is  the  nature  of  the  substances  which 
are  responsible  for  and  transmit  this  specificity  ?  It  is 
obvious  that  a  definite  answer  to  this  question  brings 
us  also  to  the  very  problem  of  evolution  as  well  as  that 
of  the  constitution  of  living  matter. 

There  can  be  no  doubt  that  on  the  basis  of  our  present 
knowledge  proteins  are  in  most  or  practically  all  cases 
the  bearers  of  this  specificity.  This  has  been  found 
out  not  only  with  the  aid  of  the  precipitin  reaction  but 
also  with  the  anaphylaxis  reaction,  by  which,  as  the 
reader  may  know,  is  meant  that  when  a  small  dose  of 
a  foreign  substance  is  introduced  into  an  animal  a 
hypersensitiveness  develops  after  a  number  of  days 
or  weeks,  so  that  a  new  injection  of  the  same  substance 
produces  serious  and  in  some  cases  fatal  effects.  This 
hypersensitiveness,  which  was  first  analysed  by  Richet,  ^ 
is  specific  for  the  substance  which  has  been  injected. 
Now  all  these  specific  reactions,  the  precipitin  reaction 
as  well  as  the  anaphylactic  reaction,  can  be  called  forth 
by  proteins.  Thus  Richet,  in  his  earliest  experiments, 
showed  that  only  the  protein-containing  part  of  the 
extract  of  actinians,  by  which  he  called  forth  anaphy- 

'  Richet,  C,  L'anaphylaxie.     Paris,  1912. 


62    Chemical  Basis  of  Genus  and  Species 

laxis,  was  able  to  produce  this  phenomenon,  and  later 
he  showed  that  it  was  generally  impossible  to  produce 
anything  resembling  anaphylaxis  by  non-protein  sub- 
stances, e.  g.,  cocain  or  apomorphin.'  Wells  isolated 
from  egg-white  four  different  proteins  (three  coagulable 
proteins  and  one  non-coagulable)  which  can  be  distin- 
guished from  each  other  by  the  anaphylaxis  reaction, 
although  all  come  from  the  same  biological  object.^ 
Michaelis  as  well  as  Wells  found  that  the  spHt  products 
of  the  protein  molecule  are  no  longer  able  to  call  forth 
the  anaphylaxis  reaction.  Since  peptic  digestion  has 
the  effect  of  annihilating  the  power  of  proteins  to  call 
forth  anaphylaxis,  we  are  forced  to  the  conclusion  that 
the  first  cleavage  products  of  proteins  have  already^ 
lost  the  power  of  calling  forth  immunity  reactions. 

A  pretty  experiment  by  Gay  and  Robertson  ^  should 
be  mentioned  in  this  connection.    Robertson  had  shown 

that  a  substance  closely  resembling  paranucleins  both  in 
its  properties  and  its  C,  H,  and  N  content  can  be  formed 
from  the  filtered  products  of  the  complete  peptic  hydro- 
lysis of  an  approximately  four  per  cent,  neutral  solution 
of  potassium  caseinate  by  the  action  of  pure  pepsin  at 
36°  C. 

He  considered  this  a  case  of  a  real  synthesis  of  proteins 
from  the  products  of  its  hydrolytic  cleavage.     This 

» Quoted  from  Wells,  H.  G.,  Jour.  Infect.  Diseases,  1908,  v.,  449. 

'Ibid.,  191 1,  ix.,  147. 

3  Gay,  F.  P.,  and  Robertson,  T.  B.,  Jour.  Biol.  Chem.,  1912,  xii.,  233. 


Chemical  Basis  of  Genus  and  Species    63 

interpretation  was  not  generally  accepted  and  received 

a  different  interpretation  by  Bayliss  and  other  workers. 
Gay  and  Robertson  were  able  to  show  that  paranuclein 
when  injected  into  an  animal  will  sensitize  guinea-pigs 
for  anaphylactic  intoxication  for  either  paranuclein 
or  casein  and  apparently  indiscriminately.  The  pro- 
ducts of  complete  peptic  digestion  of  casein  had  no 
such  effect,  but  the  synthetic  product  of  this  diges- 
tion obtained  by  Robertson's  method  has  the  same 
specific  antigenic  properties  as  paranuclein,  thus 
making  it  appear  that  Robertson  had  indeed  suc- 
ceeded in  causing  a  synthesis  of  paranuclein  with  the 
aid  of  pepsin  from  the  products  of  digestion  of  casein 
by  pepsin. 

here  are  a  few  statements  in  the  literature  to  the 
effect  that  the  specificity  of  organisms  might  be  due 
to  other  substances  than  proteins.  Thus  Bang  and 
Forssmann  claimed  that  the  substances  (antigens) 
responsible  for  the  production  of  hemolysis  were  of  a 
lipoid  nature,  but  their  statements  have  not  been  con- 
firmed, and  Fitzgerald  and  Leathes^  reached  the  con- 
clusion that  lipoids  are  non-antigenic.  Ford  claims 
to  have  obtained  proof  that  a  glucoside  contained  in 
the  poisonous  mushroom  Amanita  phalloides  can  act 
as  an  antigen.  But  aside  from  this  one  fact  we  know 
that  proteins  and  only  proteins  can  act  as  antigens  and 

'  Fitzgerald,  J.  G.,  and  Leathes,  J.  B.,  Univ.  Cal.  Pub.,  1912,  "Patho- 
logy," ii.,  39. 


64    Chemical  Basis  of  Genus  and  Species 

are  therefore  the  bearers  of  the  specificity  of  living 
organisms. 

Bradley  and  Sansum'  found  that  guinea-pigs  sensi- 
tized to  beef  or  dog  hemoglobin  fail  to  react  or  react  but 
slightly  to  hemoglobin  of  other  origin.  The  hemoglo- 
bins tried  were  dog,  beef,  cat,  rabbit,  rat,  turtle, 
pig,  horse,  calf,  goat,  sheep,  pigeon,  chicken,  and 
man. 

6.  It  would  be  of  the  greatest  importance  to  show 
directly  that  the  homologous  proteins  of  different 
species  are  different.  This  has  been  done  for  hemo- 
globins of  the  blood  by  Reichert  and  Brown,  ^  who  have 
shown  by  crystallographic  measurements  that  the 
hemoglobins  of  any  species  are  definite  substances  for 
that  species. 

The  crystals  obtained  from  different  species  of  a  genus 
are  characteristic  of  that  species,  but  differ  from  those  of 
other  species  of  the  genus  in  angles  or  axial  ratio,  in  optical 
characters,  and  especially  in  those  characters  comprised 
under  the  general  term  of  crystal  habit,  so  that  one  species 
can  usually  be  distinguished  from  another  by  its  hemoglobin 
crystals.  But  these  differences  are  not  such  as  to  preclude 
the  crystals  from  all  species  of  a  genus  being  placed  in  an 
isomorphous  series  (p.  327). 

'  Bradley,  H.  C,  and  Sansum,  W.  D.,  Jour.  Biol.  Chem.,  1914,  xviii., 

497- 

'  Reichert,  E.  T.,  and  Brown,  A.  P.,  "The  Differentiation  and  Speci- 
ficity of  Corresponding  Proteins  and  other  Vital  Substances  in  Relation 
to  Biological  Classification  and  Organic  Evolution."  Carnegie  Insti- 
tution Publication  No.  116,  Washington,  1909. 


Chemical  Basis  of  Genus  and  Species    65 

As  far  as  the  genus  is  concerned  it  was  found  that 
the  hemoglobin  crystals  of  any  genus  are  isomorphous. 

In  some  cases  this  isomorphism  may  be  extended  to 
include  several  genera,  but  this  is  not  usually  the  case, 
unless  as  in  the  case  of  dogs  and  foxes,  for  example,  the 
genera  are  very  closely  related. 

The  most  important  question  for  us  is  the  following: 
Are  the  differences  between  the  corresponding  hemo- 
globin crystals  of  different  species  of  the  same  genus 
such  as  to  warrant  the  statement  that  they  indicate 
chemical  differences?  If  this  were  the  case  we  might 
say  that  blood  reactions  as  well  as  hemoglobin  crystals 
indicate  that  differences  in  the  constitution  of  proteins 
determine  the  species  specificity  and,  perhaps,  also 
species  heredity.  The  following  sentences  by  Reichert 
and  Brown  seem  to  indicate  that  this  may  be  true  for 
the  crystals  of  hemoglobin. 

The  hemoglobins  of  any  species  are  definite  substances 
for  that  species.  But  upon  comparing  the  corresponding 
substances  (hemoglobins)  in  different  species  of  a  genus  it  is 
generally  found  that  they  differ  the  one  from  the  other  to  a 
greater  or  less  degree ;  the  differences  being  such  that  when 
complete  crystallographic  data  are  available  the  different 
species  can  be  distinguished  by  these  differences  in  their 
hemoglobins.  As  the  hemoglobins  crystallize  in  isomor- 
phous series  the  differences  between  the  angles  of  the 
crystals  of  the  species  of  a  genus  are  not,  as  a  rule,  great; 
but  they  are  as  great  as  is  usually  found  to  be  the  case  with 

5 


66    Chemical  Basis  of  Genus  and  Species 

minerals  or  chemical  salts  that  belong  to  an  isomorphous 
group  (p.  326). 

As  Professor  Brown  writes  me,  the  difficulty  in 
answering  the  question  definitely,  whether  or  not  the 
hemoglobins  of  different  species  are  chemically  different, 
lies  in  the  fact  that  there  is  as  yet  no  criterion  which 
allows  us  to  discriminate  between  a  species  and  a  JMen- 
delian  mutation  except  the  morphological  differences. 
It  is  not  impossible  that  while  species  differ  by  the  con- 
stitution of  some  or  most  of  their  proteins,  Mendelian 
heredity  has  a  different  chemical  basis. 

It  is  regrettable  that  work  like  that  of  Reichert  and 
Brown  cannot  be  extended  to  other  proteins,  but  it 
seems  from  anaphylaxis  reactions  that  we  might  expect 
results  similar  to  those  in  the  case  of  the  hemoglobins. 
The  proteins  of  the  lens  are  an  exception  inasmuch  as, 
according  to  Uhlenhuth,  the  proteins  of  the  lens  of 
mammals,  birds,  and  amphibians  cannot  be  discrimi- 
nated from  each  other  by  the  precipitin  reaction.  ^ 

7.  The  serum  of  certain  humans  may  cause  the 
destruction  or  agglutination  of  blood  corpuscles  of 
certain  other  humans.  This  fact  of  the  existence  of 
"isoagglutinins"  seems  to  have  been  established  for 
man,  but  Hektoen  states  that  he  has  not  been  able  to 
find  any  isoagglutinins  in  the  serum  of  rabbits,  guinea- 
pigs,  dogs,  horses,  and  cattle.     Landsteiner  found  the 

'  Uhknhuth,  Das  hiologische  Verfahren  zur  Erkennung  und  Unier- 
sclieidung  von  21ensclien  und  Tierhlut,  Jena,  1905,  p.  102. 


Chemical  Basis  of  Genus  and  Species    67 

remarkable  fact  that  the  sera  of  certain  individuals  of 
humans  could  hemolyze  the  corpuscles  of  certain  other 
individuals,  but  not  those  of  all  indi\'iduals.  A  system- 
atic investigation  of  this  variability  led  him  to  the 
discovery  of  three  distinct  groups  of  individuals,  the 
sera  of  each  group  acting  in  a  definite  wa}^  towards 
the  corpuscles  of  the  representatives  of  each  other 
group.  Later  obser\'ers,  for  example  Jansk}^  and  ^Moss, 
established  four  groups.  These  groups  are,  according 
to  Moss,  ^  as  follows : 

Group  I.     Sera  agglutinate  no  corpuscles. 

Corpuscles  agglutinated  by  sera  of  Groups  2,3,4. 
Group  2.     Sera  agglutinate  corpuscles  of  Groups  1,3. 

Corpuscles  agglutinated  by  sera  of  Groups  3,  4. 
Group  3.     Sera  agglutinate  corpuscles  of  Groups  1,2. 

Corpuscles  agglutinated  by  sera  of  Groups  2,  4. 
Group  4.     Sera  agglutinate  corpuscles  of  Groups  i,  2,  3. 

Corpuscles  agglutinated  by  no  serum. 

The  relative  frequency  of  the  four  groups  follows 
from  the  following  figures.  Of  one  hundred  bloods 
tested  by  Moss  in  series  of  twenty  there  were  found : 

10  belonging  to  Group  i . 

40  belonging  to  Group  2. 

7  belonging  to  Group  3. 

43  belonging  to  Group  4. 

Groups  2  and  4  are  in  the  majority  and  in  over- 
whelming numbers,  which  indicates  that,  as  a  rule,  the 

^Moss,  W.  L.,  Johns  Hopkins  Hospital  Bulletin,  1910,  xxi.,  62. 


68    Chemical  Basis  of  Genus  and  Species 

sera  agglutinate  the  blood  corpuscles  of  individuals  of 
the  other  groups,  but  not  those  of  individuals  belong- 
ing to  the  same  group.  The  phenomenon  that  a  serum 
agglutinates  no  corpuscles  (Group  i),  or  that  the  cor- 
puscles are  agglutinated  by  no  serum  (Group  4),  are 
the  exceptions.  It  is  obvious  that,  as  far  as  our  problem 
is  concerned,  only  Groups  2  and  3  are  to  be  considered. 
There  is  no  Mendelian  character  which  refers  only  to 
one  half  of  the  individuals  except  sex.  Since  nothing 
is  said  about  a  relation  of  Groups  2  and  3  to  sex  such 
a  relation  probably  does  not  exist. 

8.  The  facts  thus  far  reported  imply  the  suggestion 
that  the  heredity  of  the  genus  Is  determined  by  proteins 
of  a  definite  constitution  differing  from  the  proteins  of 
other  genera.  This  constitution  of  the  proteins  would 
therefore  be  responsible  for  the  genus  heredity.  The 
different  species  of  a  genus  have  all  the  same  genus 
proteins,  but  the  proteins  of  each  species  of  the  same 
genus  are  apparently  different  again  in  chemical  con- 
stitution and  hence  may  give  rise  to  the  specific  bio- 
logical or  immunity  reactions. 

We  may  consider  it  as  established  by  the  work  of 
McClung,  Sutton,  E.  B.Wilson,  Miss  Stevens,  Morgan, 
and  many  others,  that  the  chromosomes  are  the  carriers 
of  the  Mendelian  characters.  These  chromosomes 
occur  in  the  nucleus  of  the  egg  and  in  the  head  of  the 
sperm.  Now  the  latter  consists.  In  certain  fish,  of 
lipoids  and  a  combination  of  nucleinic  acid  and  pro- 


Chemical  Basis  of  Genus  and  Species    69 

tamlne  or  histone,  the  latter  a  non-coagulable  protein, 
more  resembling  a  split  product  of  one  of  the  larger 
coagulable  proteins. 

A.  E.  Taylor^  found  that  if  the  spermatozoa  of  the 
salmon  are  injected  into  a  rabbit,  the  blood  of  the  animal 
acquires  the  power  of  causing  cytolysis  of  salmon  sper- 
matozoa. When,  however,  the  isolated  protamines 
or  nucleinic  acid  or  the  lipoids  prepared  from  the 
same  sperm  were  injected  into  a  rabbit  no  results  of  this 
kind  were  observed.  H.  G.  Wells  more  recently  tested 
the  relative  efficiency  of  the  constituents  of  the  testes 
of  the  cod  (which  in  addition  to  the  constituents  of 
the  sperm  contained  the  proteins  of  the  testicle). 
From  the  testicle  he  prepared  a  histone  (the  protein 
body  of  the  sperm  nucleus),  a  sodium  nucleinate, 
and  from  the  sperm-free  aqueous  extract  of  the  testi- 
cles a  protein  resembling  albumin  was  separated  by 
precipitation.^ 

The  albumin  behaved  like  ordinary  serum  albumin  or 
egg  albumin,  producing  typical  and  fatal  anaphylactic  re- 
actions and  being  specific  when  tried  against  mammalian 
sera.  The  nucleinate  did  not  produce  any  reactions  when 
guinea-pigs  were  given  small  sensitizing  and  larger  intoxicat- 
ing doses  (o.i  gm.)  in  a  three  weeks'  interval;  a  result  to 
be  expected,  since  no  protein  is  present  in  the  preparation. 
The  histone  was  so  toxic  that  its  anaphylactic  properties 
could  not  be  studied. 

^Taylor,  A.  E.,  Jour.  Biol.  Chem.,  1908,  v.,  311. 
'Wells,  H.  G.,  Jour.  Infect.  Diseases,  191 1,  ix.,  166. 


70    Chemical  Basis  of  Genus  and  Species 

It  is  not  impossible  that  protamines  and  histones 
might  be  found  to  act  as  specific  antigens  if  they 
were  not  so  toxic.  The  positive  results  which  Taylor 
observed  after  injection  of  the  sperm  might  have 
been  due  to  the  proteins  contained  m  the  tail  of  the 
spermatozoa,  which  in  certain  animals  at  least  does 
not  enter  the  egg  and  hence  can  have  no  influence  on 
heredity. 

It  is  thus  doubtful  whether  or  not  any  of  the  con- 
stituents of  the  nucleus  contribute  to  the  determination 
of  the  species.  This  in  its  ultimate  consequences 
might  lead  to  the  idea  that  the  Mendelian  characters 
which  are  equally  transmitted  by  egg  and  spermatozoon, 
determine  the  individual  or  variety  heredity,  but  not 
the  genus  or  species  heredity.  It  is,  in  our  present 
state  of  knowledge,  impossible  to  cause  a  spermatozoon 
to  develop  into  an  embryo,^  while  we  can  induce  the 
egg  to  develop  into  an  embryo  without  a  spermatozoon. 
This  may  mean  that  the  protoplasm  of  the  egg  is  the 
future  embryo,  while  the  chromosomes  of  both  egg  and 
sperm  nuclei  furnish  only  the  individual  characters. 

'  Loeb,  J.,  and  Bancroft,  F.  W.,  Jour.  Exper.  Zool.,  1912,  xii.,  381. 


CHAPTER  IV 

SPECIFICITY   IN    FERTILIZATION 

I .  We  have  become  acquainted  with  two  character- 
istics of  living  matter :  the  specificity  due  to  the  specific 
proteins  characteristic  for  each  genus  and  possibly 
species  and  the  synthesis  of  living  matter  from  the 
split  products  of  their  main  constituents  instead  of 
from  a  supersaturated  solution  of  their  own  substance, 
as  is  the  case  in  crystals.  We  are  about  to  discuss  in 
this  and  the  next  chapter  a  third  characteristic,  namely, 
the  phenomenon  of  fertilization.  While  this  is  not 
found  in  all  organisms  it  is  found  in  an  overwhelming 
majority  and  especially  the  higher  organisms,  and  of 
all  the  mysteries  of  animated  nature  that  of  fertiliza- 
tion and  sex  seems  to  be  the  most  captivating,  to  judge 
from  the  space  it  occupies  in  folklore,  theology,  and 
"literature."  Bacteria,  when  furnished  the  proper 
nutritive  medium,  will  synthetize  the  specific  material 
of  their  own  body,  will  grow  and  divide,  and  this  process 
will  be  repeated  indefinitely  as  long  as  the  food  lasts 

and  the  temperature  and  other  outside  conditions  are 

71 


']2  Specificity  in  Fertilization 

normal.  It  is  purely  due  to  limitation  of  food  that 
bacteria  or  certain  species  of  them  do  not  cover  the 
whole  planet.  But,  as  every  layman  knows,  the  major- 
ity of  organisms  grow  only  to  a  certain  size,  then  die, 
and  the  propagation  takes  place  through  sex  cells  or 
gametes:  a  female  cell — the  egg — containing  a  large 
bulk  of  protoplasm  (the  future  embryo)  and  reserve 
material;  and  the  male  cell  which  in  the  case  of  the 
spermatozoon  contains  only  nuclear  material  and  no 
cytoplasmic  material  except  that  contained  in  the  tail 
which  in  some  and  possibly  many  species  does  not  enter 
the  egg.  The  male  element — the  spermatozoon — enters 
the  female  gamete — the  egg — and  this  starts  the  de- 
velopment. In  the  case  of  most  animals  the  egg  cannot 
develop  unless  the  spermatozoon  enters.  The  question 
arises:  How  does  the  spermatozoon  activate  the  egg? 
And  also  how  does  it  happen  that  the  spermatozoon 
enters  the  egg?  We  will  first  consider  the  latter  ques- 
tion. These  problems  can  be  answered  best  from  ex- 
periments on  forms  in  which  the  egg  and  the  sperm  are 
fertilized  in  sea  water.  Many  marine  animals,  from 
fishes  down  to  lower  forms,  shed  their  eggs  and  sperm 
into  the  sea  water  where  the  fertilization  of  the  egg 
takes  place,  outside  the  body  of  the  female. 

The  first  phenomenon  which  strikes  us  in  this  con- 
nection is  again  a  phenomenon  of  specificity.  The  sper- 
matozoon can,  as  a  rule,  only  enter  an  egg  of  the  same 
or  a  closely  related  species,  but  not  that  of  one  more 


Specificity  in  Fertilization  73 

distantly  related.  What  is  the  character  of  this  speci- 
ficity? The  writer  was  under  the  impression  that  a 
clue  might  be  obtained  if  artificial  means  could  be 
found  by  which  the  egg  of  one  species  might  be  fertil- 
ized with  a  distant  species  for  which  this  egg  is  natu- 
rally immune.  Such  an  experiment  would  mean  that 
the  lack  of  specificity  had  been  compensated  by  the 
artificial  means.  It  is  well  known  that  the  egg  of  the 
sea  urchin  cannot  as  a  rule  be  fertilized  with  the  sperm 
of  a  starfish  in  normal  sea  water.  The  writer  tried 
whether  this  hybridization  could  not  be  accomplished 
provided  the  constitution  of  the  sea  water  were  changed. 
He  succeeded  in  causing  the  fertilization  of  a  large 
percentage  of  the  eggs  of  the  Californian  sea  urchin, 
Strongylocentrotus  purpiiratus ,  with  the  sperm  of  various 
starfish  {e.  g.,  Asterias  ochracea)  and  Holothurians  by 
slightly  raising  the  alkalinity  of  the  sea  water,  through 
the  addition  of  some  base  (NaOH  or  tetraethylammo- 
niumhydroxide  or  various  amines) ,  the  optimumi  being 
reached  when  0.6  c.c.  N/io  NaOH  is  added  to  50  c.c. 
of  sea  water.  It  is  a  peculiar  fact  that  this  solution  is 
efficient  only  if  both  egg  and  sperm  are  together  in  the 
hyperalkaline  sea  water.  If  the  eggs  and  sperm  are 
treated  separately  with  the  hyperalkaline  sea  water  and 
are  then  brought  together  in  normal  sea  water  no  fer- 
tilization takes  place  as  a  rule,  while  with  the  same 
sperm  and  eggs  the  fertilization  is  successful  again  if 
both  are  mixed  in  the  hyperalkaline  solution.     From 


74  Specificity  in  Fertilization 

this  the  writer  concluded  that  the  fertiHzing  power 
depends  on  a  rapidly  reversible  action  of  the  alkali  on 
the  surface  of  the  two  gametes.  It  was  found  that 
an  increase  of  the  concentration  of  calcium  in  the  sea 
water  also  favoured  the  entrance  of  the  Asterias  sperm 
into  the  egg  of  purpuratus;  and  that  if  CCa  was  in- 
creased it  was  not  necessary  to  add  as  much  NaOH. 

The  spermatozoon  enters  the  egg  through  the  so- 
called  fertilization  cone,  i.  e.,  a  protoplasmic  process 
comparable  to  the  pseudopodium  of  an  amoeboid  cell. 
The  analogy  of  the  process  of  phagocytosis — i.  e.,  the 
taking  up  of  particles  by  an  amoeboid  cell — and  that  of 
the  engulfing  of  the  spermatozoon  by  the  egg  presents 
itself.  We  do  not  know  definitely  the  nature  of  the 
forces  which  act  in  the  case  of  phagocytosis — although 
surface  tension  forces  and  agglutination  have  been 
suggested ;  both  are  surface  phenomena  and  are  rapidly 
reversible. 

We  should  then  say  that  the  specificity  in  the  process 
of  fertilization  consists  in  a  peculiarity  of  the  surface 
of  the  egg  and  spermatozoon  which  in  the  case  of  S. 
purpuratus  9  and  Asterias  cf  can  be  supplied  by  a 
slight  increase  in  the  COH  or  CCa. 

By  this  method  fifty  per  cent,  or  more  of  the  eggs  of 
purpuratus  could  be  fertilized  with  the  sperm  of  the 
starfish  Asterias  ochracea,  capitata,  Ophiurians,  and 
Holothurians,  while  with  the  sperm  of  another  starfish, 
Pycnopodia  spuria,  only  five  per  cent.,  and  with  the 


Specificity  in  Fertilization  75 

sperm  of  Asteri?ia  only  one  per  cent,  could  be  fertilized.^ 
Godlewski  succeeded  by  the  same  method  in  fertilizing 
the  eggs  of  a  Naples  starfish  with  the  sperm  of  a  crinoid.  ^ 
The  writer  did  not  succeed  in  bringing  about  the  ferti- 
lization of  the  egg  of  another  sea  urchin  in  California, 
Strongylocentrotus  franciscanus,  with  the  sperm  of  a 
starfish.  Although  these  eggs  formed  a  membrane 
in  contact  with  the  sperm.,  the  latter  did  not  enter  the 
egg ;  nor  has  the  writer  as  yet  succeeded  in  causing  the 
sperm  of  Asterias  to  enter  the  egg  of  Arhacia. 

Kupelwieser^  obser\^ed  that  the  spermatozoon  of 
molluscs  may  occasionally  enter  into  the  egg  of  S. 
purpuratus  in  normal  sea  water  and  later,  at  Naples, 
he  observed  the  same  for  the  sperm  of  annehds.  In 
these  cases  no  development  took  place.  In  teleost 
fishes  the  spermatozoon  can  enter  the  eggs  of  widely 
different  species  but  with  rare  exceptions  all  the  embr}'0s 
will  die  in  an  early  stage  of  development. -^ 

2.  The  fact  that  an  increase  in  the  alkalinity  or  in 
the  concentration  of  calcium  allowed  foreign  sperm  to 
enter  the  egg  of  the  sea  urchin,  suggested  the  idea  that 
a  diminution  of  alkalinity  or  calcium  in  the  sea  w^ater 


^Loeb,  J.,  Arch.  f.  d.  ges.  Physiol.,  1903,  xcix.,  323;  1904,  civ.,  325; 
Arch.  f.  Eniwcklngsmech.,  1910,  xxx.,  II.,  44;  1914,  xl.,  310;  Science, 
1914,  xl.,  316. 

^Godlewski,  E.,  Arch.  f.  Eniwcklngsmech.,  1906,  xx.,  579. 

3  Kupelwieser,  H.,  Arch.  f.  Eniwcklngsmech.,  1909,  xxvii.,  434;  Arch. 
/.  Zellforsch.,  19 12,  viii.,  352. 

4  See  Chapter  II. 


76  Specificity  in  Fertilization 

might  block  the  entrance  of  the  sperm  of  sea  urchin  into 
eggs  of  their  own  species.  This  was  found  to  be  cor- 
rect; when  we  put  eggs  and  sperm  of  the  same  species 
of  sea  urchin  into  solutions  whose  concentration  of  Ca 
or  of  OH  is  too  small,  the  sperm,  although  it  may  be 
intensely  active,  cannot  enter  the  egg. 

For  the  purpose  of  these  experiments  the  ovaries 
and  testes  of  the  sea  urchins  were  not  put  into  sea 
water,  but  instead  into  pure  m/2NaCl  and  after  several 
washings  in  this  solution  were  kept  in  it  (they  remain 
alive  for  several  days  in  pure  m/2  NaCl).  Several 
drops  of  such  sperm  and  one  drop  of  eggs  were  in  one 
series  of  experiments  put  into  2.5  c.c.  of  a  neutral  mix- 
ture of  m/2  NaCl  and  3/8  m  MgCU  in  the  proportion  in 
which  these  two  salts  exist  in  the  sea  water.  In  such 
a  neutral  solution  eggs  of  Arbacia  or  purpuratus  are 
not  fertilized  no  matter  how  long  they  remain  in  it, 
although  the  spermatozoa  swim  around  the  eggs  very 
actively.  That  no  spermatozoon  enters  the  eggs  can 
be  shown  by  the  fact  that  the  eggs  do  not  divide  (al- 
though they  can  segment  in  such  a  solution  if  previously 
fertilized  in  sea  water  or  some  other  efficient  solution). 
When,  however,  eggs  and  sperm  are  put  into  2.5  c.c. 
of  the  same  solution  of  NaCl+MgCU,  containing  in 
addition  one  drop  of  a  N/ioo  solution  of  NaOH  (or  NH3 
or  benzylamine  or  butylamine)  or  eight  drops  of  m/ioo 
NaHCOa,  most,  and  often  practically  all  of  the  eggs 
at  once  form  fertilization  membranes  and  segment  at 


Specificity  in  Fertilization  ^^ 

the  proper  time,  indicating  that  fertiHzation  has  been 
accompHshed.  The  same  result  can  be  obtained  if  the 
eggs  are  transferred  into  a  neutral  mixture  of  NaCl+ 
MgCla+CaCla  (in  the  proportion  in  which  these  salts 
exist  in  the  sea  water)  or  into  a  neutral  mixture  of 
NaCl+MgCU+KQ+CaCU.  In  such  neutral  mix- 
tures the  eggs  form  fertilization  membranes  and  begin 
to  segment.  The  eggs  are  not  fertilized  in  a  neutral 
solution  of  NaCl  or  of  NaCl+KCl.^ 

It  is,  therefore,  obvious  that  if  we  diminish  the  al- 
kalinity of  the  solution  surrounding  the  egg  and  deprive 
this  solution  of  CaCU  we  estabUsh  the  same  block  to  the 
entrance  of  the  spermatozoon  of  Arbacia  into  the  egg 
of  the  same  species  as  exists  in  normal  sea  water  for 
the  entrance  of  the  sperm  of  the  starfish  into  the  egg  of 
purpuratus. 

The  "block"  created  in  this  way,  to  the  entrance  of 
the  sperm  of  Arbacia  into  the  egg  of  the  same  species 
is  also  rapidly  reversible. 

..^'We  reach  the  conclusion,  therefore,  that  the  speci- 
ficity which  allows  the  sperm  to  enter  an  egg  is  a  sur- 
face effect  which  can  be  increased  or  diminished  by  an 
increase  or  diminution  in  the  concentration  of  OH  as 
well  as  of  Ca.  The  writer  has  shown  that  an  increase 
in  the  concentration  of  both  substances  may  cause  an 
agglutination  of  the  spermatozoa  of   starfish  to   the 

'  Loeb,  J.,  Science,  1914,  xl.,  316;  Am.  Naturalist,  1915,  xlix., 
257- 


78  Specificity  in  Fertilization 

jelly  which  surrounds  the  egg  of  purpuratus.^  It  is 
thus  not  impossible  that  the  specificity  which  favours 
the  entrance  of  a  spermatozoon  into  an  egg  of  its  own 
species  may  consist  in  an  agglutination  between  sper- 
matozoon and  egg  protoplasm  (or  its  fertilization  cone) ; 
and  that  this  agglutination  is  favoured  if  the  Coh  or 
Cca  or  both  are  increased  within  certain  limits.         ,  -"^ 

Godlewski  discovered  a  very  interesting  form  of  block 
to  the  entrance  of  the  spermatozoon  into  the  egg  which 
takes  place  if  two  different  types  of  sperm  are  mixed. 
He  had  found  that  the  sperm  of  the  annelid  Choetopteriis 
is  able  to  enter  the  egg  of  the  sea  urchin  and  that  in 
so  doing  it  causes  membrane  formation.  The  egg, 
however,  does  not  develop  but  dies  rapidly,  as  is  the 
case  when  we  induce  artificial  membrane  formation,  as 
we  shall  see  in  the  next  chapter. 

Godlewski  found  that  if  the  sperm  of  ChcEtopterus  and 
the  sperm  of  sea  urchins  are  mixed  the  mixture  is  not 
able  to  induce  development  or  membrane  formation, 
since  now  neither  spermatozoon  can  enter ;  blood  has  the 
same  inhibiting  effect  as  the  foreign  sperm.  The  mix- 
ture does  not  interfere  with  the  development  of  the 
eggs  if  they  are  previously  fertilized.^ 

The  phenomenon  was  further  investigated  by  Her- 
lant^  who  found  that  if  the  sperm  of  a  sea  urchin  is 

'  Loeb,  Arch.  f.  Entwcklngsmech.,  1914,  xl.,  310. 
'Godlewski,  E.,  Arch.  f.  Entwcklngsmech.,  191 1,  xxxiii.,  196. 
3  Herlant,  M.,  Anat.  Anzeiger,  1912,  xlii.,  563. 


Specificity  in  Fertilization  79 

mixed  with  the  sperm  of  certain  annelids  {ChcBtoptems) 
or  molluscs,  and  if  after  some  time  the  eggs  of  the 
sea  urchin  are  added  to  the  mixture  of  the  two  kinds 
of  sperm  no  egg  is  fertilized.  If,  however,  the  solution 
is  subsequently  diluted  with  sea  water  or  if  the  egg 
that  was  in  this  mixture  is  washed  in  sea  water,  the 
same  sperm  mixture  in  which  the  egg  previously  re- 
mained unfertiHzed  will  now  fertilize  the  egg.  From 
these  and  similar  observations  Herlant  draws  the  con- 
clusion that  the  block  existed  at  the  surface  of  the  egg, 
inasmuch  as  a  reaction  product  of  the  two  t3^pes  of 
sperm  is  formed  after  some  time  which  alters  the  sur- 
face of  the  egg  and  thereby  prevents  the  sperm  from 
entering.  This  view  is  supported  not  only  by  all  the 
experiments  but  also  by  the  observation  of  the  writer 
that  foreign  sperm  or  blood  is  able  to  cause  a  real  agglu- 
tination after  some  time  if  mixed  with  the  sperm  of  a 
sea  urchin  or  a  starfish.^  We  can  imagine  that  the 
precipitate  forms  a  film  around  the  egg  and  acts  as  a 
block  for  the  agglutination  between  egg  and  spermato- 
zoon. The  block  can  be  removed  mechanically  by 
washing. 

3.  The  fact  has  been  mentioned  that  the  most 
motile  sperm  will  not  be  able  to  enter  into  the  egg  if 
certain  other  conditions  (specificity  or  COH  or  Cca) 
are  not  fulfilled.  On  the  other  hand,  living  but  immo- 
bile sperm  cannot  enter  the  egg  under  any  conditions. 

'  Loeb,  J.,  Jour.  Exper.  ZooL,  1914,  xvii.,  123. 


8o  Specificity  in  Fertilization 

If  we  add  a  trace  of  KCN  to  the  sperm  of  Arhacia  so 
that  the  spermatozoon  becomes  immobile  no  egg  is 
fertilized  even  if  the  eggs  and  the  sperm  are  thoroughly- 
shaken  together;  while  the  same  spermatozoa  will 
fertilize  these  eggs  as  soon  as  the  HCN  has  evaporated 
and  they  again  become  motile.  It  was  formerly- 
thought  that  the  spermatozoon  had  to  bore  itself  into 
the  egg,  being  propelled  by  the  movements  of  the 
flagellum.  It  is,  however,  more  probable  that  only 
a  certain  energy  of  vibration  is  needed  on  the  part  of 
the  spermatozoon  to  make  the  latter  stick  to  the  surface 
of  the  egg  and  agglutinate  and  that  later  forces  of  a 
different  character  bring  the  spermatozoon  into  the 
egg.  The  fact  that  under  normal  conditions  a  very 
slight  degree  of  motility  on  the  part  of  the  spermatozoon 
allows  it  to  enter  the  egg  of  its  own  species  seems  to 
favour  such  a  view. 

It  is  a  common  experience  that  spermatozoa  become 
very  active  when  they  reach  the  neighbourhood  of  an 
egg.  V.  Dungern  assumed  that  only  foreign  sperm 
became  thus  active,  but  F.  R.  Lillie'  has  pointed  out 
that  this  may  be  a  specific  effect.  The  writer  tested 
this  idea  on  the  sperm  and  eggs  of  two  species  of  star- 
fish and  of  sea  urchins.  It  should  be  mentioned  that 
the  eggs  of  the  starfish  used  in  this  experiment  were 
completely  immature  and  could  not  be  fertilized,  while 
the  eggs  of  the  sea  urchins  were  mature.     The  testicles 

'  Lillie,  F.  R.,  Jour.  Exper.  ZooL,  1914,  xvi.,  523. 


Specificity  in  Fertilization  8i 

and  ovaries  had  been  kept  in  NaCl  and  all  the  sperm 
was  immotile.  Eggs  and  sperm  were  mixed  together 
in  a  pure  m/2  NaCl  solution  where  the  sperm  was 
only  rendered  motile  by  the  proximity  of  eggs.  The 
following  table  gives  the  result.  ^ 

TABLE  V 
Specificity  of  Activation  of  Sperm  by  Eggs 


Asteriasd^ 

Asterinad' 

Fra  ncisca- 

P  urpura- 

tusd^ 

Asterias   9 

Immediately 

No 

Moderately 

Slight    effect 

(immature) 

very  motile. 

activation. 

active. 

m  mame- 
diate  con- 
tact    with 

Asterina9 

Not  motile. 

Violent  activ- 

Violent activ- 

egg- 
Slight    effect 

(immature) 

ity. 

ity. 

only  near 
the  egg. 

Franciscanus  9 

Slightly  mo- 

No motility. 

Immediately 

Immediately 

(mature) 

tile. 

active. 

active. 

Purpuratus  9 

Slightly  mo- 

Slight   effect 

Immediately 

Immediately 

(mature) 

tile    after 
some  time. 

in  immedi- 
ate contact 
with  eggs. 

active. 

active. 

The  spermatozoa  of  starfish  show  a  marked  speci- 
ficity inasmuch  as  they  are  strongly  activated  only  by 
the  eggs  of  their  own  species,  although  in  this  experi- 
ment these  were  immature,  and  to  a  slight  degree  only 
by  the  eggs  of  the  sea  urchin  purpuratus.  But  it  is 
also  obvious  that  the  specificity  is  far  from  exclusive 
since  the  immature  eggs  of  Asterina  activate  the  sperm 
of  the  sea  urchin  jranciscaniis  as  powerfully  as  is  done 

'Loeb,  J.,  Am.  Naturalist,  1915,  xlix.,  257. 
6 


82  specificity  in  Fertilization 

by  the  mature  eggs  of  the  sea  urchin  purpuratus  and 
franciscanus.  In  studying  these  results  the  reader  must 
keep  in  mind  first  that  all  these  experiments  were  made 
in  a  NaCl  solution  and  second  that  it  requires  a  stronger 
influence  to  activate  the  spermatozoa  of  the  starfish, 
which  are  not  motile  at  first  even  in  sea  water,  than 
the  sea  urchin  spermatozoa  which  are  from  the  first 
very  active  in  such  sea  water,  and  which  may  there- 
fore be  considered  as  being  at  the  threshold  of  activity 
in  pure  NaCl  solution. 

Wasteneys  and  the  writer  (in  experiments  not  yet 
published)  did  not  succeed  in  demonstrating  an  activat- 
ing effect  of  the  eggs  of  various  marine  teleosts  upon 
sperm  of  the  same  species. 

4.  F.  R.  Lillie'  has  studied  the  very  striking  phe- 
nomenon of  transitory  sperm  agglutination  which 
takes  place  when  the  sperm  of  a  sea  urchin  or  of 
certain  annelids  is  put  into  the  supernatant  sea  water 
of  eggs  of  the  same  species.  If  we  put  one  or  more 
drops  of  a  very  thick  sperm  suspension  of  the  Cali- 
fornian  sea  urchin  S.  purpuratus  carefully  into  the 
centre  of  a  dish  containing  3  c.c.  of  ordinary  sea  water 
and  let  the  drop  stand  for  one-half  to  one  minute  and 
then  by  gentle  agitation  mix  the  sperm  with  the  sea 
water  the  mass  of  thick  sperm  which  is  at  first  rather 
viscous  is  distributed  equally  in  sea  water  in  a  few 

'  Lillie,  F.  R.,  Science,  1913,  xxxviii.,  524;  Jour.  Exper.  ZooL,  1914, 
xvi.,  523;  Biol.  Bull.,  1915,  xxviii.,  18. 


Specificity  in  Fertilization  83 

seconds  and  the  result  is  a  homogeneous  sperm  sus- 
pension. When,  however,  the  same  experiment  is 
made  with  the  sea  water  which  has  been  standing  for 
a  short  time  over  a  large  mass  of  eggs  of  the  same  spe- 
cies, the  thick  drop  of  sperm  seems  to  be  less  miscible 
and  instead  of  a  homogeneous  suspension  we  get,  as  a 
result,  the  formation  of  a  large  number  of  distinct 
clusters  which  are  visible  to  the  naked  eye  and  which 
may  possess  a  diameter  of  i  or  2  mm.  The  rest  of  the 
sea  water  is  almost  free  from  sperm.  These  clusters 
of  spermatozoa  may  last  for  from  two  to  ten  minutes 
and  then  dissolve  by  the  gradual  detachment  of  the 
spermatozoa  from  the  periphery  of  the  cluster. 

This  phenomenon  seems  to  occur  in  sea  urchins  and 
annelids.  The  writer  has  vainly  looked  for  it  in  differ- 
ent forms  of  the  Califomian  starfish  or  molluscs  and 
in  fish  at  Woods  Hole.  Lillie  failed  to  find  it  in  the 
starfish  at  Woods  Hole. 

The  writer  found  that  the  sperm  of  the  Califomian 
sea  urchin  Strongylocentrotus  purpuratus  will  form  clus- 
ters with  the  egg  sea  water  of  purpuratus  but  not  with 
that  oifranciscanus;  while  the  sperm  oifranciscanus  will 
agglutinate  with  the  egg  sea  water  of  both  species, 
but  the  clusters  last  a  little  longer  with  the  eggs  of 
its  own  species. 

He  also  found  that  the  clusters  are  more  durable  in 
a  neutral  than  in  a  slightly  alkaline  solution  and  that 
the    agglutination    disappears    the    more    rapidly    the 


84  Specificity  in  Fertilization 

more  alkaline  the  solution.  The  presence  of  bivalent 
cations,  especially  Ca,  also  favours  the  agglutination. 

It  was  also  found  that  this  agglutination  occurs 
only  when  the  spermatozoa  are  very  motile;  thus  if  a 
trace  of  KCN  is  added  to  a  mass  of  thick  sea-urchin 
sperm  so  that  the  spermatozoa  become  immotile  a 
drop  of  this  sperm  will  not  agglutinate  when  put  in  egg 
sea  water  of  the  same  species;  while  later,  after  the 
HCN  has  evaporated,  the  same  sperm  will  agglutinate 
when  put  into  such  sea  water. 

The  writer  suggests  the  following  explanation  of 
the  phenomenon.  The  egg  sea  water  contains  a  sub- 
stance which  forms  a  precipitate  with  a  substance  on 
the  surface  of  the  spermatozoon  whereby  the  latter 
becomes  slightly  sticky.  This  precipitate  is  slowly 
soluble  in  sea  water  and  the  more  rapidly  the  more 
alkaline  (within  certain  Hmits).  Only  when  the 
spermatozoa  run  against  each  other  with  a  certain  im- 
pact will  they  stick  together,  as  LilHe  suggested.  Lillie 
assumes  that  this  agglutinating  substance  contained 
in  egg  sea  water  is  required  to  bring  about  fertilization 
and  he  therefore  calls  it  "fertilizin." '  But  this  assump- 
tion seems  to  go  beyond  the  facts  inasmuch  as  the 
existence  of  such  an  agglutinating  substance  can  only 
be  proved  in  a  few  species  of  animals  (sea  urchins  and 
annehds);  and  as,  moreover,  sea-urchin  sperm  can 
fertilize  eggs  which  will  not  cause  the  sperm  to  agglu- 

•  Lillie,  F.  R.,  loc.  cil. 


Specificity  in  Fertilization  85 

tinate,  e.  g.,  the  egg  of  franciscanus  can  be  fertilized 
by  sperm  of  purpuratus,  although  the  egg  sea  water 
oi  franciscanus  causes  no  agglutination  of  the  sperm  of 
purpuratus.  When  the  jelly  surrounding  the  egg  of 
the  Californian  sea  urchin  S.  purpuratus  is  dissolved 
with  acid  and  the  eggs  are  washed,  the  eggs  will  not 
cause  any  more  sperm  agglutination;  and  yet  one  hun- 
dred per  cent,  of  such  eggs  can  be  fertilized  by  sperm.  ^ 
5.  It  is  well  known  that  if  an  egg  is  once  fertilized 
it  becomes  impermeable  for  other  spermatozoa.  This 
cannot  well  be  due  to  the  fact  that  the  egg  develops; 
for  the  writer  found  some  time  ago  that  eggs  of  Strofz- 
gylocentrotus  purpuratus  which  are  induced  to  develop 
by  means  of  artificial  parthenogenesis  can  be  fertilized 
by  sperm.  The  following  observation  leaves  no  doubts 
in  this  respect.  When  the  unfertilized  eggs  of  pur- 
puratus are  put  for  two  hours  into  hypertonic  sea  water 
(50  c.c.  of  sea  water+8  c.c.  23/^  m  NaCl)  and  then  trans- 
ferred into  sea  water  it  occasionally  happens  that  a 
certain  percentage  of  the  eggs  will  begin  to  divide  into 
2,  4,  8  or  more  cells,  without  developing  any  further. 
When  to  such  eggs  after  they  have  remained  in  the 
resting  stage  for  a  number  of  hours  or  a  day,  sperm  is 
added,  some  or  all  of  the  blastomeres  form  a  fertiliza- 
tion membrane  and  now  begin  to  develop  into  larvae; 
and  if  the  spermatozoon  gets  into  a  blastomere  of  the 

'  Loeb,  J.,  Jour.  Exper.  ZooL,  1914,  xvii.,  123;  Am.  Naturalist,  1915, 
xlix.,  257. 


86  Specificity  in  Fertilization 

2-  or  4-cell  stage  normal  plutei  will  result.  When  the 
sperm  is  added  while  the  eggs  are  in  active  partheno- 
genetic  cell  division  the  individual  blastomeres  into 
which  a  spermatozoon  enters  will  also  form  a  fertiliza- 
tion membrane,  but  such  blastomeres  perish  very 
rapidly.  It  is  not  yet  possible  to  state  why  it  should 
make  such  a  difference  for  the  possibility  of  develop- 
ment whether  the  spermatozoon  enters  into  a  blasto- 
mere  when  at  rest  or  when  it  is  in  active  nuclear  division, 
although  the  idea  presents  itself  that  in  the  latter  case 
an  abnormal  mix-up  and  separation  of  chromosomes 
and  other  constituents  may  be  responsible  for  the  fatal 
result.  Whatever  may  be  the  explanation  of  this 
phenomenon  it  proves  to  us  that  it  is  not  the  process 
of  development  in  itself  which  acts  as  a  block  to  the 
entrance  of  a  spermatozoon  into  an  egg  which  is  already 
fertilized.  ^ 

When  the  spermatozoon  enters  the  egg  of  the  sea 
urchin  it  calls  forth  the  formation  of  a  membrane — 
the  fertilization  membrane.  It  might  be  considered 
possible  that  this  membrane  formation  or  the  alteration 
underlying  or  accompanying  it  is  responsible  for  the 
fact  that  an  egg  once  fertilized  becomes  immune  against 
a  spermatozoon.  We  shall  see  in  the  next  chapter 
that  it  is  possible  to  call  forth  the  membrane  in  an 
unfertilized  sea-urchin  egg  by  treating  it  with  butyric 

'  Loeb,  J.,  Arch.  f.  Entivcklngsmech.,  1907,  xxii.,  479;  Artificial  Par- 
thenogenesis  and  Fertilizalioti,  Chicago,  19 13,  p.  240. 


Specificity  in  Fertilization  87 

acid.  This  membrane  is  so  tough  in  the  egg  of  Stro7i- 
gylocentrotus  that  no  spermatozoon  can  get  through 
it;  in  the  egg  of  Arhacia  the  membrane  is  occasionally 
replaced  by  a  soft  gelatinous  film.  If  no  second  treat- 
ment is  given  to  such  eggs  they  will  disintegrate  in  a 
comparatively  short  time,  but  when  sperm  is  added 
some  or  most  of  the  eggs  will  develop  in  the  way  charac- 
teristic of  fertilized  eggs.  ^  When  the  membrane  is  too 
tough  to  allow  the  spermatozoon  to  enter  the  egg  it 
can  be  shown  that  if  the  membrane  is  torn  mechanically 
the  egg  can  still  be  fertilized  by  sperm. 

Should  it  be  possible  that  the  spermatozoon  can  no 
longer  agglutinate  with  the  fertilized  egg  or  that  those 
phagocytotic  reactions  which  we  suppose  to  play  a 
role  in  the  entrance  of  the  spermatozoon  into  the  egg 
are  no  longer  possible  after  a  spermatozoon  has  entered? 
The  mere  fact  of  development  is  apparently  not  the 
cause  which  bars  a  spermatozoon  from  entering  an 
egg  already  fertilized  by  sperm. 

Lillie  assumes  that  the  egg  loses  its  "fertilizin"  in 
the  process  of  membrane  formation  since  the  sea  water 
containing  such  eggs  no  longer  gives  the  agglutinin 
reaction  with  sperm,  and  he  believes  that  the  lack  of 
"fertilizin"  in  the  fertilized  egg  or  in  the  egg  after 
membrane  formation  is  the  cause  of  the  block  in  the 
fertiUzed  egg.     But  we  have  seen  that  the  artificial 

'  Loeb,  J.,  Science,  1913,  xxxviii.,  749;  Arch.  f.  Entwcklngsmech., 
1914,  xxxviii.,  277;  Wasteneys,  H.,  Jour.  Biol.  Chem.,  1916,  xxiv.,  281. 


88  Specificity  in  Fertilization 

membrane  formation  does  not  create  such  a  block  al- 
though it  puts  an  end  to  the  "fertilizin"  reaction.  In 
the  egg  of  purpuratus  the  "fertilizin"  reaction  ceases 
when  the  jelly  surrounding  the  egg  is  dissolved  by  an 
acid  and  the  eggs  are  repeatedly  washed;  yet  such  eggs 
can  easily  be  fertilized  bj''  sperm. 

Lillie  does  not  assume  that  the  "fertilizin"  causes 
an  agglutination  between  egg  and  spermatozoon — we 
should  assent  to  such  an  assumption — but  that  the 
"fertilizin"  acts  like  an  "amboceptor"  between  egg 
and  spermatozoon,  the  latter  being  the  complement, 
the  former  the  antigen.  The  pathologist  would  prob- 
ably object  to  this  interpretation  since  no  "ambocep- 
tor" is  needed  for  agglutination.  The  writer  has  had 
some  doubts  concerning  the  value  of  Ehrlich's  side- 
chain  theory  which,  besides,  can  only  be  applied  in  a 
metaphorical  sense  to  the  mechanism  of  the  entrance 
of  the  spermatozoon  into  the  egg.^ 

'  Loeb,  J.,  Ajn.  Naturalist,  1915,  xlix.,  257. 

Tlie  writer  may  be  permitted  to  illustrate  by  a  special  case  his  reason 
for  declining  to  accept  Ehrlich's  side-chain  theory.  Ehrlich  and  Sachs 
found  that  if  to  a  given  mass  of  toxin  small  quantities  of  antitoxin  are 
added  successively  the  first  fraction  added  neutralized  more  than  the 
later  fractions;  and  on  the  basis  of  this  reasoning  Ehrlich  concluded 
that  ten  different  toxins  were  contained  in  the  diphtheria  toxin.  Ar- 
rhenius  showed  that  the  same  phenomenon  can  be  obtained  when  a 
weak  base  like  NH4OH  is  neutralized  by  a  weak  acid  (e.  g.,  boric 
acid);  hence  we  should  assume  that  NH4OH  consists  of  ten  different 
forms  of  ammonia.  Both  cases,  the  saturation  of  toxin  with  anti- 
toxin and  ammonia  with  boric  acid  are  equilibrium  phenomena. 
(Arrhenius,  S.,  Quantitative  Laws  in  Biological  Cliemistry,  London, 
1915-) 


Specificity  in  Fertilization  89 

6.  The  reason  that  an  egg  once  fertihzed  with 
sperm  cannot  be  fertilized  again  may  be  found  in  a 
group  of  facts  which  we  will  now  discuss,  namely,  the 
self-sterility  of  many  hermaphrodites.  The  fact  that 
hermaphrodites  are  often  self-sterile,  while  their  eggs 
can  be  fertilized  with  sperm  from  a  different  individual 
of  the  same  species  has  played  a  great  role  in  the 
theories  of  evolution.  We  are  here  only  concerned 
with  the  mechanism  which  determines  the  block  to 
the  entrance  of  a  spermatozoon  into  an  egg  of  the 
same  hermaphroditic  individual. 

Castle^  observed  and  studied  the  phenomenon  of 
self -sterility  in  an  Ascidian,  Cio7ia  intestinalis,  which  is 
hermaphroditic.  Animals  which  were  kept  isolated 
discharged  both  eggs  and  sperm  into  the  surrounding 
sea  water.  Often  no  egg  was  fertilized,  but  in  some 
cases  five,  ten,  or  as  many  as  fifty  per  cent,  of  the  eggs 
could  be  successfully  fertilized  with  sperm  from  the 
same  individual;  while  if  several  individuals  were  put 
into  the  same  dish  as  a  rule  one  hundred  per  cent,  of 
the  eggs  which  were  discharged  segmented.  Morgan^ 
found  that  the  eggs  of  various  females  differ  in  their 
power  of  being  fertilized  by  sperm  of  the  same  in-^ 
dividual  while  one  hundred  per  cent,  could  usually  be 
fertilized  with  sperm   of   a   different   individual.     He 

^Castle,  W.  E.,  Bull.  Miis.  Comp.  Zool.,  Harvard,  1896,  xxvii.,  203. 
=  Morgan,  T.  H.,  Jour.  Exper.  Zool.,  1904,  i.,  135;  Arch.f.  Entivcklngs- 
mech.,  1910,  XXX.,  206. 


90  Specificity  in  Fertilization 

found  in  addition  that  if  the  eggs  of  Ciona  are  put  for 
about  ten  minutes  into  a  two  per  cent,  ether  solution 
in  sea  water  in  a  number  of  cases  the  percentage  of 
eggs  fertilized  by  sperm  of  the  same  individual  shows 
a  slight  increase.  Fuchs'  has  reported  results  similar 
to  those  of  Castle  and  Morgan. 

A  new  point  of  attack  has  been  introduced  into  the 
work  of  self-sterility  in  plants  by  the  consideration 
of  heredity.  Darwin  found  that  in  Reseda  which  is 
monoecious  (or  hermaphroditic)  certain  individuals  are 
either  completely  self -sterile  or  completely  self-f  ertile ; 
and  Compton  showed  that  apparently  self-fertility 
is  a  Mendelian  dominant  to  self -sterility.^ 

According  to  Jost  this  self-sterility  in  hermaphroditic 
plants  is  due  to  the  fact  that  if  pollen  of  the  same  plant 
is  used  the  normal  growth  of  the  pollen  tube  is  inhibited, 
while  this  inhibition  does  not  exist  for  pollen  from  a 
different  individual.  Correns  calls  these  substances 
which  prevent  the  adequate  growth  of  pollen,  "inhibit- 
ory" substances,  and  finds  that  they  can  apparently 
be  transmitted  to  the  offspring.  He  made  experiments 
on  Cardamine  pratensis  which  is  self -sterile.  ^  He  fertil- 
ized two  individuals  of  Cardamine  crosswise  and  raised 
sixty  plants  of  the  first  generation.  He  compared  the 
fertility  of  these  F  i  plants  toward  (a)  their  parents,  and 

»Fuchs,  H.  M.,  Jour.  Genet.,  1915,  iv.,  215. 

'  Quoted  from  Fuchs. 

J  Correns,  C,  Biol.  Centralbl.,  1913,  xxxiii.,  389. 


Specificity  in  Fertilization  91 

(Z>)  foreign  plants.  All  the  fertilizations  with  the  foreign 
plants  were  successful,  but  the  fertilizations  with  the 
parents  were  only  partly  successful.  According  to 
their  reaction  they  could  be  divided  into  four  groups : 

(A)  fertile  with  both  parents.     Type  bg 

(B)  fertile  with  one  (B),  sterile  with  the  other  parent  (G). 

(a)  fertile  with  B,  sterile  with  G.     Type  bG 

(b)  fertile  with  G,  sterile  with  B.     Type  Bg 

(C)  sterile  with  both  parents.     Type  BG 

It  was  found  that  approximately  fifteen  of  the  sixty 
children  belonged  to  each  of  the  four  groups.  This 
should  be  expected  if  the  inhibitory  substance  to  each 
parent  is  transmitted  to  the  children  independently. 
Half  of  the  children  will  thus  inherit  the  inhibitory 
substance  of  one  parent  and  the  other  half  will  inherit 
the  inhibitory  substance  of  the  other  parent.  This 
agrees  with  the  assumption  that  there  are  definite 
determiners  for  the  inhibitory  substances  in  the  child- 
ren which  will  be  transmitted  to  half  of  the  children. 
Rather  complicated  assumptions  are  needed  to  explain 
all  the  facts  observed  by  Correns  on  this  basis  and  since 
the  subject  is  still  under  investigation  we  need  not  go 
further  into  the  details. 

To  us  the  assumption  and  experimental  support  of 
the  idea  that  self-sterility  is  caused  by  the  presence  of 
a  substance  inhibitory  to  the  entrance  of  a  spermato- 
zoon is  important.     Should  it  be  possible  that  the  block 


92  Specificity  in  Fertilization 

created  by  the  entrance  of  a  spermatozoon  into  the 
egg  is  also  due  to  an  inhibitory  substance  carried  by  a 
spermatozoon  into  the  egg;  and  furthermore  that  the 
effect  of  the  inhibitory  substance  should  be  the  pre- 
vention of  further  agglutination  of  the  spermatozoon 
with  the  egg  or  of  the  growth  of  the  pollen  tube  in 
plants?  On  such  an  assumption  self-sterility  would  be 
due  to  a  lack  of  agglutination  between  the  egg  of  a 
Hermaphrodite  and  a  spermatozoon  of  the  same  indiv- 
idual. The  experiments  on  the  agglutinins  have  shown 
that  while  isoagglutinins  {i.  e.,  agglutinins  for  other 
individuals  of  the  same  species)  are  common  auto- 
agglutinins  {i.  e.,  agglutinins  for  cells  of  the  same  indi- 
vidual) rarely  if  ever  occur, 

7.  A  positive  chemotropism  of  the  spermatozoa 
toward  an  egg  of  the  same  species  has  been  demon- 
strated in  a  few  cases,  but  it  seems  that  this  pheno- 
menon is  not  determined  by  that  type  of  substances 
which  give  rise  to  species  specificity.  The  famous 
experiment  of  Pfeffer  on  the  spermatozoa  of  ferns 
inaugurates  this  line  of  investigation.  He  found  that 
such  spermatozoa  when  moving  in  a  straight  hne 
through  the  water  will  be  deviated  in  their  course 
if  they  come  near  an  archegonium;  they  will  then 
turn  toward  it,  enter  it,  and  enter  the  egg.  Pfeffer 
showed  that  o.oi  per  cent,  malic  acid  if  put  into 
a  capillary  tube  will  attract  the  spermatozoa  of 
ferns. 


Specificity  in  Fertilization  93 

When  the  liquid  in  the  tube  contains  only  o.oi  per  cent, 
malic  acid  the  spermatozoa  of  ferns  very  soon  move  toward 
the  opening  of  the  capillary  tube  and  within  from  five  to 
ten  minutes  many  hundreds  of  spermatozoa  may  accumu- 
late in  the  tube.  The  malic  acid  acts  as  well  in  the  form 
of  a  free  acid  as  in  the  form  of  salts.* 


These  experiments  were  continued  and  amplified  by 
Shibata.  Bruchmann^  found  that  the  spermatozoa 
of  Lycopodium  are  positively  chemotactic  to  citric  acid 
and  salts  of  this  acid,  although  no  citric  acid  could  be 
shown  in  the  contents  of  the  archegonia.  They  are 
also  positively  chemotactic  to  the  watery  extract  from 
archegonia. 

Dewitz,  BuUer,  and  the  writer  have  vainly  tried  to 
prove  the  existence  of  a  positive  chemotropism  of 
spermatozoa  to  eggs  of  the  same  species.  Lillie  claims 
to  have  proved  a  positive  chemotropism  of  the  sperm 
of  sea  urchins  to  "fertilizin, "  but  such  a  conclusion  is 
only  justified  if  a  method  similar  to  that  of  Pfeffer's 
with  capillary  tubes,  gives  positive  results;  such  a 
method  was  not  used  in  Lillie's  experiments.  It  seems 
that  the  fertilization  of  the  egg  by  sperm  is  rendered 
possible  by  two  facts ;  first  that  where  fertilization  takes 
place  outside  the  body  egg  and  sperm  are  shed  simul- 
taneously by  the  two  sexes.     This  can  be  easily  ob- 


'^  Pfeffer,  Untersuchungen  aus  dem  botanischen  Institut  zu  Tubingen, 
1881-1885,  i.,  363. 

"Bruchmann,  H.,  Flora,  1909,  ic,  193. 


94  Specificity  in  Fertilization 

served  in  the  case  of  fish.  But  it  is  also  the  case  in 
invertebrates.  Thus  the  writer  has  observed  that  the 
sea  urchins  Strongylocentrotus  purpuratus  at  the  shore 
of  Pacific  Grove  all  spawn  simultaneously.  The 
examination  extended  over  several  miles  of  shore. 
At  such  spawning  seasons  the  sea  water  becomes  a 
suspension  of  sperm. 

The  second  fact  guaranteeing  the  fertilization  of  the 
eggs  is  the  overwhelming  excess  of  spermatozoa  over 
eggs.  The  enormous  waste  in  animated  nature  is  in 
agreement  with  the  idea  of  a  lack  of  purpose;  since 
in  this  case  the  laws  of  chance  must  play  a  great 
role;  and  the  origin  of  durable  organisms  by  laws  of 
chance  is  only  comprehensible  on  the  basis  of  an 
enormous  wastefulness,  for  which  evidence  is  not 
lacking. 


CHAPTER  V 

ARTIFICIAL   PARTHENOGENESIS 

I.  The  majority  of  eggs  cannot  develop  unless  they 
are  fertilized,  that  is  to  say,  unless  a  spermatozoon 
enters  into  the  egg.  The  question  arises:  How  does 
the  spermatozoon  cause  the  egg  to  develop  into  a  new 
organism?  The  spermatozoon  is  a  living  organism 
with  a  complicated  structure  and  it  is  impossible  to 
explain  the  causation  of  the  development  of  the  egg 
from  the  structure  of  the  spermatozoon.  No  progress 
was  possible  in  this  field  until  ways  were  found  to 
replace  the  action  of  the  living  spermatozoon  by  well- 
known  physicochemical  agencies.^  Various  observers 
such  as  Tichomiroff,  R.  Hertwig,  and  T.  H.  Morgan 
had  found  that  unfertilized  eggs  may  begin  to  segment 
imder  certain  conditions,  but  such  eggs  always  disin- 
tegrated in  their  experiments  without  giving  rise  to 
larvae.     In  1899  the  writer  succeeded  in  causing  the 

^  The  substitution  of  well-known  physicochemical  agencies  for  the 
mysterious  action  of  the  spermatozoon  was  the  task  the  writer  set 
himself  in  this  work  and  not  the  explanation  of  natural  parthenogenesis, 
as  the  author  of  a  recent  text-book  seems  to  assume. 

95 


96  Artificial  Parthenogenesis 

unfertilized  eggs  of  the  sea  urchin  Arhacia  to  develop 
into  swimming  larvse,  blastulae,  gastrulas,  and  plutei, 
by  treating  them  with  hypertonic  sea  water  of  a  definite 
osmotic  pressure  for  about  two  hours.  When  such 
eggs  were  then  put  back  into  normal  sea  water  many 
segmented  and  a  certain  percentage  developed  into 
perfectly  normal  larvae,  blastulas,  gastrulas,  and  plutei.  * 
Soon  afterward  this  was  accomplished  by  other  methods 
for  the  unfertilized  eggs  of  a  large  number  of  marine 
animals,  such  as  starfish,  molluscs,  and  annelids.  None 
of  these  eggs  can  develop  under  normal  conditions 
unless  a  spermatozoon  enters.  These  experiments 
furnished  proof  that  the  activating  effect  of  the  sper- 
matozoon upon  the  egg  can  be  replaced  by  a  purely 
physicochemical  agency.  ^ 

The  first  method  used  in  the  production  of  larvae 
from  the  unfertilized  eggs  did  not  lend  itself  to  an 
analysis  of  the  activating  effect  of  the  spermatozoon 
upon  the  egg,  since  nothing  was  known  about  the  action 
of  a  hypertonic  solution,  except  that  it  withdraws 
water  from  the  egg;  and  there  was  no  indication  that 
the  entrance  of  the  spermatozoon  causes  the  egg  to  lose 
water.  No  further  progress  was  possible  until  another 
method  of  artificial  parthenogenesis  was  found.  When 
a  spermatozoon  enters  the  egg  of  a  sea  urchin  or  starfish 

'  Loeb.  J.,  Am.  Jour.  Physiol.,  1899,  iii.,  135;  1900,  iii.,  434. 
*  Loeb,  J.,  Artificial  Parthenogenesis  and  Fertilization,  Chicago,  1913. 
The  reader  is  referred  to  this  bock  for  the  literature  on  the  subject. 


Artificial  Parthenogenesis 


97 


or  certain  annelids,  the  surface  of  the  egg  undergoes 
a  change  which  is  called  membrane  formation;  and 
which  consists  in  the  appearance  of  a  fine  membrane 
around  the  egg,  separated  from  the  latter  by  a  liquid 
(Figs.  4  and  5).     O.  and  R.  Hertwig  and  Herbst  had 


Fig.  4  Fig.  5 

Fig.   4.     Unfertilized  egg  surrounded  by  spermatozoa   (whose 

flagellum  is  omitted  in  the  drawing). 
Fig.  5.     The  same  egg  after  a  spermatozoon  has  entered.     The 

fertilization  membrane  is  separated  from  the  egg  by  a  clear 

space. 

observed  that  such  a  membrane  could  be  produced  in 
an  unfertilized  egg  if  the  latter  was  put  into  chloroform 
or  xylol,  but  such  eggs  perished  at  once.  It  was  gene- 
rally assumed,  moreover,  that  the  process  of  membrane 
formation  was  of  no  significance  in  the  phenomenon  of 
fertilization,  except  perhaps  that  the  fertilization  mem- 
brane guarded  the  fertilized  egg  against  a  further 
invasion  by  sperm.  However,  since  the  fertilized  egg 
is  protected  against  this  possibility  by  other  means 
the  membrane  is  hardly  needed  for  such  a  purpose. 


98  Artificial  Parthenogenesis 

In  1905  the  writer  found  that  membrane  formation, 
or  rather  the  change  of  the  surface  of  the  egg  under- 
lying the  membrane  formation,  is  the  essential  feature 
in  the  activation  of  the  egg  by  a  spermatozoon.  He 
observed  that  when  unfertilized  eggs  of  the  Californian 
sea  urchin  Strongylocentrotus  purpuratus  are  put  for 
from  one  and  a  half  to  three  minutes  into  a  mixture  of 
50  c.c.  of  sea  water+2.6  c.c.  N/io  acetic  or  propionic 
or  butyric  or  valerianic  acid  and  are  then  put  into 
normal  sea  water  all  or  the  majority  of  the  eggs  form 
membranes;  and  that  such  eggs  when  the  temperature 
is  very  low  will  segment  once  or  repeatedly  and  may 
even — if  the  temperature  is  as  low  as  4°C.  or  less — 
develop  into  swimming  blastulse^;  but  they  will  then 
disintegrate.  On  the  other  hand,  if  they  are  kept  at 
room  temperature  they  will  develop  only  as  far  as  the 
aster  formation  and  nuclear  division  and  then  begin 
to  disintegrate.  It  should  be  mentioned  that  the  time 
which  elapses  between  artificial  membrane  formation 
and  nuclear  division  is  greater  than  that  between  the 
entrance  of  a  spermatozoon  and  nuclear  division. 

It  was  obvious,  therefore,  that  artificial  membrane 
formation  induced  by  butyric  acid  initiates  the  processes 
underlying  development  of  the  egg  but  that  for  some 
reason  the  egg  is  sickly  and  perishes  rapidly. 

When,  however,  such  eggs  were  given  a  short  treat- 

'  The  reader  will  find  a  description  of  the  development  of  this  egg  in 
the  next  chapter. 


Artificial  Parthenogenesis  99 

ment  with  hypertonic  sea  water  or  with  lack  of  oxygen 
or  with  KCN  they  developed  into  normal  larv^. 
This  new  or  improved  method  of  artificial  partheno- 
genesis is  as  follows:  The  eggs  are  put  for  from  two  to 
four  minutes  into  50  c.c.  sea  water  containing  a  certain 
amount  of  N/io  butyric  acid  (2.6  c.c.  in  the  case  of  S. 
purpuratus  in  California  and  2.0  c.c.  in  the  case  of 
Arhacia  in  Woods  Hole).  Ten  or  fifteen  minutes  later 
the  eggs  are  put  into  hypertonic  sea  water  (50  c.c.  sea 
water+S  c.c.  2^^  m  NaCl  or  Ringer  solution  or  cane 
sugar)  in  which  they  remain,  at  15^  C.  from  thirty-five 
to  sixty  minutes  in  the  case  of  purpuratus,  and  from 
17^  minutes  to  22^4  minutes  at  23°  in  the  case  of 
Arhacia  at  Woods  Hole.  If  the  eggs  are  then  trans- 
ferred to  normal  sea  water  they  will  develop.  In 
making  these  experiments,  which  have  been  repeated 
and  confirmed  by  numerous  investigators,  it  should  be 
remembered  that  this  effect  of  the  hypertonic  solution 
has  a  high  temperature  coefficient  (about  two  for 
10°  C.)  and  that  a  slight  overexposure  to  the  hyper- 
tonic sea  water  injures  the  eggs  so  that  development  is 
abnormal.  By  this  method  it  is  possible  to  imitate  the 
activating  effect  of  the  living  spermatozoon  upon  the 
egg  in  every  detail  and  eggs  treated  in  this  way  will 
develop  in  large  numbers  into  perfectly  normal  larvs. 
We  shall  see  later  that  they  can  also  be  raised  to  the 
adult  state. 

2.     The  next  task  was  to  find  out  the  nature  of  the 


100  Artificial  Parthenogenesis 

action  of  the  two  agencies  upon  the  development  of  the 
egg.  It  soon  became  obvious  that  the  membrane 
formation  (or  the  alteration  underlying  membrane 
formation)  was  the  more  important  of  the  two,  since  in 
the  eggs  of  starfish  and  annelids  this  was  sufficient  for 
the  production  of  larvse ;  and  that  the  second  treatment 
had  only  the  corrective  effect,  of  overcoming  the  sickly 
condition  in  which  mere  membrane  formation  had  left 
the  eggs.  It  was,  therefore,  of  great  interest  to  ascer- 
tain what  substances  or  agencies  caused  membrane 
formation  in  the  egg,  since  it  now  became  clear  that 
the  spermatozoon  could  only  cause  membrane  formation 
by  carrying  one  such  substance  into  the  egg.  These 
investigations  led  the  writer  to  the  result  that  all  those 
substances  and  agencies  which  are  known  to  cause 
cytolysis  or  hemolysis  (see  Chapter  III)  will  also  induce 
membrane  formation,  and  that  the  essential  feature  in 
the  causation  of  development  is  a  cytolysis  of  the 
superficial  or  cortical  layer  of  the  egg.  As  soon  as 
this  layer  is  destroyed  the  development  of  the  egg  can 


The  substances  and  agencies  which  cause  cytolysis  and 
hence,  if  their  action  is  restricted  to  the  surface  of  the 
egg,  will  induce  development  are,  besides  the  fatty  acids : 
(i)  saponin  or  solanin  or  bile  salts;  (2)  the  solvents  of 
lipoids,  benzol,  toluol,  amylene,  chloroform,  aldehyde, 
ether,  alcohols,  etc.;  (3)  bases;  (4)  hypertonic  or  hypo- 
tonic solutions;  (5)  rise  in  temperature,  and  (6)  certain 


Artificial  Parthenogenesis  loi 

salts,  e.  g.,  BaCla  and  SrCla  in  the  case  of  the  egg  of 
purpuratus,  and  according  to  R.  Lillie,  Nal  or  NaCNS 
in  the  egg  of  Arhacia.  Whenever  we  submit  an  unfer- 
tilized sea-urchin  egg  to  an}^  of  these  agencies  and 
restrict  the  cytolysis  to  the  superficial  or  cortical  layer 
of  the  egg  {i.  e.,  if  we  transfer  the  egg  to  normal  sea 
water  before  the  cytolytic  agent  has  had  time  to  diffuse 
into  the  main  egg)  the  egg  will  form  a  membrane  and 
behave  as  if  the  membrane  formation  had  been  called 
forth  by  a  fatty  acid,  with  this  difference  only,  that 
the  various  agencies  are  not  all  equally  harmless  for  the 
egg.'  -^' 

If  the  idea  was  correct  that  the  change  imderlying 
membrane  formation  was  essentially  a  cytolysis  of  the 
cortical  layer  of  the  egg,  it  was  to  be  expected  (from  the 
data  contained  in  Chapter  III)  that  the  blood  serum 
or  the  cell  extracts  of  foreign  species  would  also  cause 
membrane  formation  and  thus  induce  the  development 
of  the  unfertilized  egg,  while  serum  of  animals  of  the 
same  species  or  genus  would  have  no  such  effects.  This 
was  found  to  be  correct.  In  1907  the  writer  showed 
that  the  blood  serum  of  a  Gephyrean  worm,  Dendro- 
stoma,  was  able  to  cause  membrane  formation  in  the 
egg  of  the  sea  urchin.  When  added  in  a  dilution  of 
I  c.c.  of  serum  to  500  or  1000  c.c.  of  sea  water  to  eggs  of 
purpuratus  a  certain  number  formed  fertilization  mem- 
branes.    It  was  found  later  that  the  serum  and  tissue 

*  The  reader  is  referred  for  details  to  the  writer's  book  on  the  subject. 


102  Artificial  Parthenogenesis 

extracts  of  a  large  number  of  animals,  especially  of 
mammals  (rabbit,  pig,  ox,  etc.),  had  the  same  effect, 
though  it  was  necessary  to  use  higher  concentrations, 
one-half  sea  water  and  one-half  isotonic  blood  serum. 
The  eggs  of  every  female  sea  urchin,  however,  did  not 
give  the  reaction  and  not  all  the  eggs  even  of  sensitive 
females  formed  membranes.  The  writer  found,  how- 
ever, that  it  was  possible  to  increase  the  susceptibility 
of  the  eggs  against  foreign  blood  seruln  by  putting  them 
into  a  3/8  m  solution  of  SrCU  for  from  five  to  ten 
minutes  (or  possibly  a  little  longer)  before  exposing 
them  to  the  foreign  blood  serum.  BaCl  2  acts  similarly. 
The  fact  that  vSrCU  alone  can  cause  membrane  forma- 
tion in  unfertilized  eggs  if  they  are  left  long  enough  in 
the  solution  suggests  that  the  sensitizing  effect  of  the 
substance  consists  in  a  modification  of  the  cortical 
layer  similar  to  that  underlying  membrane  formation; 
and  that  the  subliminal  effect  of  a  short  treatment 
with  SrCU  and  the  subliminal  effect  of  the  foreign 
serum  when  combined  suffice  to  bring  about  the 
membrane  formation. 

Not  only  the  watery  extract  of  foreign  cells  but  also 
that  of  foreign  sperm,  induces  mem.brane  formation 
in  the  sea-urchin  egg.  The  watery  extract  of  sperm 
of  starjRsh  is  especially  active,  but  the  degree  of  activity 
varies  considerably  with  the  species  of  starfish  from 
which  the  sperm  is  taken.  The  eggs  of  different  species 
of  sea  urchins  also  show  a  different  degree  of  suscepti- 


Artificial  Parthenogenesis  103 

bility  for  the  sperm  of  foreign  species.  Thus  the  eggs 
of  Strongylocentrotus  purpuratus  require  a  higher  con- 
centration of  sperm  extract  than  the  eggs  of  5".  Jran- 
ciscanus.  For  the  latter  the  amount  of  foreign  cell 
constituents  which  suffices  to  call  forth  membrane 
formation  is  so  small  that  contact  with  almost  any 
foreign  living  spermatozoon  produces  this  effect;  and 
as  a  rule  no  previous  sensitizing  action  of  SrCL  is 
required.  When  we  bring  the  unfertilized  eggs  of  S. 
franciscanus  into  contact  with  the  living  sperm  of  star- 
fish or  shark  or  even  of  fowl,  the  eggs  form  a  fertiliza- 
tion membrane  without  previous  sensitization.  A 
specific  substance  from  the  foreign  spermatozoon 
causes  membrane  formation  before  the  spermatozoon 
has  time  to  enter  the  egg.  The  effect  is  the  same  as  if 
artificial  membrane  formation  had  been  called  forth 
with  butyric  acid,  i.  e.,  they  begin  to  develop  and 
then  disintegrate  unless  they  receive  a  second  short 
treatment. 

When,  however,  we  treat  the  eggs  with  the  watery 
extracts  from  the  cells  of  their  own  or  closely  related 
species  we  find  that  these  extracts  are  utterly  inactive, 
even  if  used  in  comparatively  strong  concentrations. 
This  agrees  with  the  results  given  in  Chapter  III. 

These  phenomena  lead  to  a  very  paradoxical  result; 
namely  that  while  in  the  case  of  foreign  sperm  we  can 
cause  membrane  formation  by  both  the  living  and  the 
dead  spermatozoon,  only  the  living  spermatozoon  of 


104  Artificial  Parthenogenesis 

the  same  species  can  induce  membrane  formation. 
This  might  find  its  explanation  on  the  assumption 
that  the  active  substance  contained  in  the  foreign 
sperm  or  serum  is  water-soluble  and  a  protein,  while 
the  activating  or  membrane-forming  substance  in  the 
spermatozoon  is  insoluble  in  water  but  soluble  in  the 
egg  (or  in  lipoids).  If  this  assumption  is  correct 
the  two  substances  are  essentially  different. 

Robertson'  has  succeeded  in  extracting  a  substance 
from  the  sperm  of  the  sea  urchin  which  causes  mem- 
brane formation  of  the  sea-urchin  egg  after  the  latter 
has  been  sensitized  by  a  treatment  with  SrCla.  It 
seems  to  the  writer  that  if  the  substance  extracted  by 
Robertson  were  the  real  fertilizing  agent  contained  in 
the  spermatozoon  it  should  fertilize  the  egg  without  a 
previous  sensitization  of  the  egg  with  SiCU  being 
required. 

3.  The  action  of  acids  in  the  mechanism  of  artificial 
parthenogenesis  provides  some  interesting  physiological 
problems.  When  unfertilized  sea-urchin  eggs  are  left 
in  sea  water  containing  any  of  the  lower  fatty  acids  up 
to  capronic,  the  eggs  will  form  no  membranes,  while 
in  such  sea  water,  and  they  will  show  no  outer  signs  of 
cytolysis  (swelling).  When,  however,  the  eggs  are 
left  in  sea  water  containing  any  of  the  fatty  acids  from 
heptylic  upward  the  eggs  will  form  membranes  while 
in  the  acid  sea  water  and  soon  afterward  will  cytolyze 

'Robertson,  T.  B.,  Arch.  f.  Entwcklngsmech.,  1912,  xxxv.,  64. 


Artificial  Parthenogenesis  105 

completely  and  swell  enormously.  In  solutions  of  the 
mineral  acids  no  membranes  are  formed  and  none  are 
formed  as  a  rule  when  the  eggs  are  transferred  back  to 
sea  water.  When  both  a  mineral  and  a  lower  fatty  acid, 
e.  g.,  butyric,  are  added  to  sea  water  the  mineral  acid 
acts  as  if  it  were  not  present,  i.  e.,  the  eggs  form  mem- 
branes when  transferred  back  to  sea  water  if  the  con- 
centration of  the  butyric  acid  is  high  enough.  All 
these  data  are  comprehensible  if  we  assume  that  only 
that  part  of  the  acid  causes  membrane  formation  which 
is  lipoid  soluble,  while  the  water  soluble  part  is  not 
involved  in  the  process  of  membrane  formation;  and 
that  the  cytolysis  or  swelling  of  the  whole  egg  can  only 
take  place  in  the  higher  fatty  acids  (heptylic  or  above) 
which  are  little  soluble  in  water  and  very  soluble  in 
lipoids,  while  the  lower  fatty  acids,  whose  water  solubil- 
ity is  comparatively  high,  can  only  bring  about  a  cyto- 
lysis and  swelling  in  the  cortical  layer  but  not  in  the 
rest  of  the  egg.  This  makes  it  appear  as  though  the 
part  undergoing  an  alteration  in  membrane  formation 
was  a  lipoid ;  and  this  would  harmonize  with  the  assump- 
tion that  the  specific  membrane-inducing  substance 
in  the  spermatozoon  is  not  soluble  in  water,  but  soluble 
in  fat. 

4.  These  and  other  observations  led  the  writer  to 
the  view  that  the  essential  process  which  causes  de- 
velopment might  be  an  alteration  of  the  surface  of  the 
egg,  in  all  probability  an  alteration  of  the  superficial 


io6  Artificial  Parthenogenesis 

layer  probably  of  the  nature  of  a  superficial  cytolysis. 
The  question  remains:  What  could  be  the  physico- 
chemical  nature  of  this  cytolysis?  The  writer  had 
suggested  in  former  papers  that  in  the  cytolysis  under- 
lying membrane  formation  lipoids  were  dissolved,  and 
he  supposed  that  the  substance  to  be  dissolved  might 
be  a  calcium-lipoid  compound  which  might  form  a 
continuous  layer  under  the  surface  of  the  egg.'  v. 
Knaffl,  working  on  the  cytolysis  of  eggs  in  the  writer's 
laboratory,  gave  the  following  idea  of  the  process : 

Protoplasm  is  rich  in  lipoids;  probably  it  is  mainly  an 
emulsion  of  these  and  proteins.  Any  physical  or  chemical 
stimulus  which  can  liquefy  the  lipoids  causes  cytolysis  of 
the  egg.  The  protein  of  the  egg  can  really  only  swell  or 
be  dissolved  if  the  condition  of  aggregation  of  the  lipoid 
is  altered  by  chemical  or  physical  agencies.  The  mechan- 
ism of  cytolysis  consists  in  the  liquefaction  of  the  lipoids 
and  thereupon  the  lipoid-free  protein  swells  or  is  dissolved 
by  taking  up  water.  .  .  .  Hence  this  supports  Loeb's  view 
that  membrane  formation  is  induced  by  the  liquefaction 
of  lipoids.^ 

The  writer  suggested  that  the  destruction  of  an 
emulsion  in  the  cortical  layer  might  possibly  be  the 
essential  feature  of  the  alteration  leading  to  membrane 
formation  and  development.  It  had  been  long  ob- 
served that  unfertilized  starfish  eggs  may  begin   to 

'  Loeb,  J.,  Uber  den  chemischen  Charakter  des  Befruchtungsvorgangs, 
etc.,  Leipzig,  1908. 

*  V.  Knaffl,  E.,  Arch.  f.  d.  ges.  Physiol.,  1908,  cxxiii.,  279. 


Artificial  Parthenogenesis  107 

develop  apparently  without  any  outside  ''stimulus," 
and  A.  P.  Mathews  found  that  slight  mechanical  agita- 
tion of  these  eggs  in  sea  water  increased  the  number 
which  developed.  It  has  been  shown  in  numerous 
experiments  by  Delage,  R.  S.  Lillie,  and  the  writer, 
that  the  substances  causing  development  in  the 
starfish  egg  are  identical  or  closely  related  to  those 
which  bring  about  this  effect  in  the  egg  of  the  sea  ur- 
chin and  in  both  cases  the  development  is  preceded 
by  a  membrane  formation. 

But  how  can  membrane  formation  be  produced  by  mere 
agitation?  It  seems  to  me  that  this  can  be  understood  if 
we  suppose  that  it  depends  upon  the  destruction  of  an 
emulsion  in  the  cortical  layer  of  the  egg.  It  is  conceivable 
that  in  the  egg  of  certain  forms  the  stability  of  this  emulsion 
is  so  small  that  mere  shaking  would  be  enough  to  destroy 
it  and  thus  induce  membrane  formation  and  development.^ 

The  durability  of  emulsions  varies,  and  where  an  emul- 
sion is  very  durable  shaking  has  no  effect,  while  where 
it  is  at  the  critical  point  of  separating  into  two  con- 
tinuous phases  a  sHght  shaking  will  bring  about  the 
separation,  and  where  the  emulsion  is  still  less  durable 
we  observe  the  phenomenon  of  a  "spontaneous" 
parthenogenesis.  Eggs  like  those  of  most  sea  urchins 
belong  to  the  former,  eggs  Hke  those  of  some  starfish 
and  annehds  belong  to  the  second  or  third  type. 

It  is  impossible  to  state  at  present  whether  the  fertil- 

'  Loeb,  J.,  Artificial  Parthenogenesis  and  Fertilization,  p.  255. 


io8  Artificial  Parthenogenesis 

ization  membrane  is  preformed  in  the  fertilized  egg  and 
merely  lifted  off  from  the  egg  or  whether  its  formation 
is  due  to  the  hardening  of  a  colloidal  substance  sepa- 
rated from  the  emulsion  (or  excreted)  and  hardened  in 
touch  with  sea  water.  But  we  can  be  sure  of  one  thing, 
namely,  that  the  liquid  between  egg  and  membrane 
contains  some  colloidal  substance  which  determines 
the  tension  and  spherical  shape  of  the  membrane.  The 
membrane  is  obviously  permeable  not  only  to  water  but 
also  to  dissolved  crystalloids,  while  it  is  impermeable 
to  colloids.  When  we  add  some  colloidal  solution 
{e.  g.,  white  of  egg,  blood  serum,  or  tannic  acid)  to  the 
sea  water  containing  fertilized  eggs  of  purpuratus,  the 
membrane  collapses  and  lies  close  around  the  egg; 
while  if  the  eggs  are  put  back  into  sea  water  or  a  sugar 
solution  the  membrane  soon  assumes  its  spherical 
shape.  This  is  intelligible  on  the  assumption  that  in 
the  process  of  membrane  formation  (or  in  the  destruc- 
tion of  the  emulsion  in  the  cortical  layer)  a  colloidal 
substance  goes  into  solution  which  cannot  diffuse  into 
the  sea  water  since  the  membrane  is  impermeable  to 
the  colloidal  particles.  The  membrane  is,  however, 
permeable  to  the  constituents  of  sea  water  or  to  sugar. 
Consequently  sea  water  will  diffuse  into  the  space 
between  membrane  and  egg  until  the  tension  of  the 
membrane  equals  the  osmotic  pressure  of  the  colloid 
dissolved  in  the  space  between  egg  and  the  membrane. 
If  we  add  enough  colloid  to  the  outside  solution  so  that 


Artificial  Parthenogenesis  109 

its  osmotic  pressure  is  higher  than  that  of  the  colloidal 
solution  inside  the  membrane  the  latter  will  collapse. 

It  should  also  be  stated  that  the  unfertilized  eggs 
of  many  marine  animals  are  surrounded  by  a  jelly 
(chorion)  which  is  dissolved  when  the  egg  is  fertilized.  ^ 
The  writer  has  shown  that  the  same  chemical  substances 
which  will  induce  membrane  formation  and  artificial 
parthenogenesis  will  as  a  rule  also  cause  a  swelling  and 
liquefaction  of  the  chorion. 

We  have  devoted  so  much  space  to  the  mechanism 
of  membrane  formation  since  it  is  likely  to  give  a  clearer 
insight  into  the  physicochemical  nature  of  physiological 
processes  than  the  phenomena  of  muscular  stimulation 
and  contraction  or  nerve  stimulation,  upon  which  the 
majority  of  physiologists  base  their  conclusions  con- 
cerning the  mechanism  of  life  phenomena. 

Before  we  come  to  the  discussion  of  the  second  factor 
in  the  activation  of  the  egg  it  should  be  stated  more 
definitely  that  for  the  eggs  of  some  forms  the  first 
factor,  the  process  underlying  membrane  formation, 
suffices  for  the  development  of  the  egg  into  a  larva  and 
that  no  second  factor  is  required  in  these  cases.  This 
is  true  for  the  eggs  of  starfish  and  certain  anneUds. 

^  It  has  been  stated  by  several  writers  that  the  eggs  of  the  sea  urchin 
can  no  longer  form  the  fertilization  membrane  when  the  jelly  surround- 
ing the  egg  is  dissolved.  The  writer  has  found  that  if  the  jelly  sur- 
rounding the  eggs  of  Strongylocentrohis  purpuratus  is  dissolved  by  acid 
the  eggs  still  form  a  fertilization  membrane  upon  the  entrance  of  a 
spermatozoon. 


no  Artificial  Parthenogenesis 

Thus  in  1901  Loeb'  and  Neilson  showed  that  a  short 
treatment  with  HCl  and  HNO3  sufficed  to  cause  some 
eggs  of  Asterias  in  Woods  Hole  to  develop  into  larvae 
without  a  second  treatment  being  needed,  and  Delage^ 
showed  the  same  for  CO2;  and  in  1905  the  writer  found 
that  the  eggs  of  the  Calif ornian  starfish  Asterina  can 
be  induced  to  form  a  membrane  by  butyric  acid  treat- 
ment and  that  ten  per  cent,  of  these  eggs  developed 
into  normal  larvae.  Quite  recently  R.  S.  Lillie  ob- 
served that  the  eggs  of  Asterias  at  Woods  Hole  can  be 
caused  to  form  membranes  and  develop  into  larvae  by 
a  treatment  with  butyric  acid  and  that  the  time  of  ex- 
posure required  to  get  a  maximal  number  of  larvae  varies 
approximately  inversely  with  the  concentration  of  the 
acid,  within  a  range  of  0.0005  to  0.006  N  butyric  acid. 
If  the  exposure  is  too  short  membrane  formation  will 
occur  without  normal  development.  ^ 

All  this  leads  us  to  the  conclusion  that  the  main 
effect  of  the  spermatozoon  in  inducing  the  development 
of  the  egg  consists  in  an  alteration  of  the  surface  of  the 
latter  which  is  apparently  of  the  nature  of  a  cytolysis 
of  the  cortical  layer.  Anything  that  causes  this  altera- 
tion without  endangering  the  rest  of  the  egg  may  induce 
its  development.     The  spermatozoon,  therefore,  causes 

*  Loeb,  J.,  Artificial  Parthenogenesis  and  Fertilization,  1913,  p.  250 
and#. 

'  Delage,  Y.,  Arch.  d.  Zool.  exper.  et  gen.,  1902,  x.,  213;  1904,  ii.,  27; 
1905,  iii.,  104. 

3  Lillie,  R.  S.,  Jour.  Biol.  Chem.,  1916,  xxiv.,  233. 


Artificial  Parthenogenesis  iii 

the  development  of  the  egg  by  carrying  a  substance 
into  the  latter  which  effects  an  alteration  of  its  surface 
layer. 

5.  We  will  now  discuss  the  action  of  the  second, 
corrective  factor,  in  the  inducement  of  development. 
When  we  cause  membrane  formation  in  a  sea-urchin 
egg  by  the  proper  treatment  with  butyric  acid  it  will 
commence  to  develop  and  segment  but  will  disinte- 
grate rapidly  if  kept  at  room  temperature  and  the 
more  rapidly  the  higher  the  temperature.  If,  however, 
the  eggs  are  treated  afterward  for  a  certain  length  of 
time  (from  thirty-five  to  sixty  minutes  at  15°  C.  for 
purpuratus  and  173^2  to  22'}/2  minutes  for  Arbacia  at 
23°  C.)  in  a  solution  which  is  isosmotic  with  50  c.c.  sea 
water  -{-8  c.c.  2^^  m  NaCl, '  they  will  develop  into  larvae, 
many  of  which  may  be  normal.  Any  hypertonic  solu- 
tion of  this  osmotic  pressure,  sea  water,  sugar,  or  a  single 
salt,  will  suffice  provided  the  solution  does  not  contain 
substances  that  are  too  destructive  for  living  matter. 
The  hypertonic  solution  produces  its  corrective  effect 
only  if  the  egg  contains  free  oxygen;  and  in  a  slightly 
alkaline  medium  more  rapidly  than  in  a  neutral  medium. 
The  time  of  exposure  in  the  hypertonic  solution  dimin- 

^  It  is  necessary  to  call  attention  to  the  fact  that  sugar  solutions  of  a 
high  concentration  (e.  g.,  m  solutions)  have  a  much  higher  osmotic 
pressure  than  that  which  they  should  have  theoretically  (Lord  Berkeley 
and  Hartley).  Delage  by  ignoring  this  fact  has  misinterpreted  his 
experiments  with  sugar  solutions.  See  Lloyd,  D.  J.,  Arch.f.  Entwcklng:- 
tnech.,  1914,  xxxviii.,  402. 


112  Artificial  Parthenogenesis 

ishes  in  certain  limits  with  the  concentration  of  OH 
ions  in  the  solution. 

It  is  strange  that  in  the  eggs  of  purpuratus  the  cor- 
rective effect  can  also  be  brought  about  by  exposing 
the  eggs  after  the  artificial  membrane  formation  for 
about  three  hours  to  normal  sea  water  free  from  oxygen; 
or  to  sea  water  in  which  the  oxidations  have  been  re- 
tarded by  the  addition  of  KCN.  This  method  is  not 
so  reliable  as  the  treatment  with  hypertonic  solution. 
,  What  does  the  hypertonic  solution  do  to  prevent  the 
disintegration  of  the  egg  after  the  artificial  membrane 
formation?  The  writer  suggested  in  1905  that  the  arti- 
ficial membrane  formation  alone  starts  the  develop- 
ment but  leaves  the  eggs  usually  in  a  sickly  condition 
and  that  the  hypertonic  solution  or  the  lack  of  oxygen 
allows  them  to  recuperate  from  such  a  condition.  The 
second  factor  is,  according  to  this  view,  merely  a  cor- 
rective or  curative  factor.  The  following  observations 
will  explain  the  reasons  for  such  an  assumption. 

The  writer  found  that  if  we  keep  the  unfertilized 
eggs  after  artificial  membrane  formation  in  sea  water 
deprived  of  oxygen  the  disintegration  of  the  egg  fol- 
lowing artificial  membrane  formation  is  prevented  for 
a  day  at  least.  The  same  result  can  be  obtained  by 
adding  ten  drops  of  ro  per  cent.  KCN  to  50  c.c.  of 
sea  water,  and  certain  narcotics,  e.  g.,  chloral  hydrate, 
act  in  the  same  way.  Wasteneys  and  the  writer  found 
that  chloral  hydrate  (and  other  narcotics)  in  the  con- 


Artificial  Parthenogenesis  113 

centration  required  do  not  suppress  or  even  lower  the 
oxidations  in  the  egg  to  any  considerable  extent,^  but 
they  prevent  the  processes  of  cell  division.  Hence  it 
seems  that  the  egg  disintegrates  so  rapidly  after  arti- 
ficial membrane  formation  because  it  is  killed  by  those 
processes  leading  to  nuclear  division  or  cell  division 
which  are  induced  by  the  artificial  membrane  forma- 
tion. If  we  suppress  these  phenomena  of  development 
(for  not  too  long  a  time)  we  give  the  egg  a  chance  to 
recover  and  if  now  the  impulse  to  develop  is  still  active 
we  notice  a  perfectly  normal  development.  If  the  egg 
is  kept  too  long  without  oxygen  it  suffers  for  other 
reasons  and  cannot  develop ;  the  writer  has  shown  that 
if  eggs  fertilized  by  sperm  are  kept  for  too  long  a  time 
without  oxygen  they  also  will  no  longer  be  able  to 
develop  normally.  The  short  treatment  with  a  hyper- 
tonic solution  supplies  the  corrective  factor  required,  so 
that  the  egg  can  then  undergo  cell  division  at  room 
temperature  without  disintegrating. 

The  correctness  of  this  interpretation,  which  is  in 
reality  mainly  a  statement  of  observations,  is  proved 
by  the  two  following  groups  of  facts.  The  older  ob- 
servers had  already  noticed  that  the  unfertiHzed  eggs 
of  the  sea  urchin  when  lying  in  sea  water  will  die  after 
a  day  or  more,  and  that  occasionally  such  eggs  show 
nuclear  division  or  even  the  beginning  of  ceU  division 

*  Loeb,  J.,  and  Wasteneys,  H.,  Jour.  Biol.  Chem.,  1913,  xiv.,  517; 
Biochem.  Zlschr.,  1913,  Ivi.,  295. 
8 


114  Artificial  Parthenogenesis 

shortly  before  disintegration  sets  in.  The  writer  has 
studied  this  phenomenon  in  the  unfertilized  eggs  of 
purpuratus  and  found  that  only  the  eggs  of  certain 
females  show  this  cell  division  before  disintegration 
and  that  the  cell  division  is  preceded  by  an  atypical 
form  of  membrane  formation;  the  eggs  surrounding 
themselves  by  a  fine  gelatinous  film  comparable  to 
that  produced  in  the  egg  of  Arbacia  by  a  treatment  with 
butyric  acid.  It  is  difficult  to  state  what  induces  the 
alteration  of  the  surface  in  the  eggs  that  lie  so  long  in 
sea  water.  It  may  be  due  to  the  CO  2  formed  by  the 
eggs — since  we  know  that  CO  2  may  induce  membrane 
formation — or  it  may  be  due  to  the  alkalinity  of  the 
sea  water  or  to  a  substance  originating  from  the  jelly 
surrounding  the  eggs.  It  was  found  that  if  such  eggs 
are  kept  without  oxygen  their  disintegration  (and  cell 
division)  will  be  delayed  considerably.  The  presum- 
able explanation  for  this  is  that  the  lack  of  oxygen  pre- 
vents the  internal  changes  underlying  cell  division  and 
thus  prevents  the  disintegration  of  the  egg.  The  direct 
proof  that  an  egg  in  the  process  of  cell  division  is  more 
endangered  by  abnormal  solutions  than  an  egg  at  rest 
has  been  furnished  by  numerous  observations  of  the 
writer.  He  showed  in  1906  that  the  fertilized  egg  of 
purpuratus  dies  rather  rapidly  in  a  pure  m/2  NaCl 
or  any  other  abnormal  isotonic  solution,  while  the  unfer- 
tilized egg  can  live  for  days  in  such  solutions.^      In 

*  Loeb,  J.,  Biochem.  Ztschr.,  1906,  ii.,  81. 


Artificial  Parthenogenesis  115 

a  series  of  papers,  beginning  in  1905,  he  showed  that 
the  fertilized  egg  will  live  longer  in  hypertonic,  hypo- 
tonic, and  otherwise  abnormally  constituted  solutions 
when  the  cell  divisions  are  suppressed  by  lack  of  oxygen 
or  by  the  addition  of  KCN  or  of  chloral  hydrate. '  It 
is  thus  obvious  that  coincident  with  the  changes  under- 
lying nuclear  division  or  cell  division  alterations  occur 
in  the  sensitiveness  of  the  egg  to  salt  solutions  of  ab- 
normal concentration  or  constitution,  e.  g.,  NaCl+CaCla 
isotonic  with  sea  water,  hypertonic,  or  hypotonic 
solutions. 

We  must,  therefore,  conclude  that  artificial  mem- 
brane formation  induces  development  but  that  it 
leaves  the  egg  in  a  sickly  condition  in  which  the  very 
processes  leading  to  cell  division  bring  about  its  de- 
struction; that  if  it  is  given  time  it  can  recover  from 
this  condition  and  that  the  treatment  with  the  hyper- 
tonic solution  also  brings  about  this  recovery  rapidly 
and  reliably. 

Herlanf  suggested  that  the  corrective  effect  of  the 
hypertonic  solution  consisted  in  the  proper  develop- 
ment of  the  astrospheres  required  for  cell  division. 
According  to  this  author  mere  membrane  formation 
does  not  lead  to  the  formation  of  sufficiently  large 
astrospheres  and  hence  cell  division  may  remain  im- 

*  Loeb,  J.,  Arch.  f.  d.  ges.  Physiol.,  1906,  cxiii.,  487;  Biochem.  Ztschr.^ 
1910,  xxvi.,  279,  289;  xxvii.,  304;  xxix.,  80;  Arch.  f.  Entwcklngsmech., 
I914,  xl.,  322.  '  Herlant,  M.,  Arch,  de  Biol.,  1913,  xxviii.,  505. 


ii6  Artificial  Parthenoeenesis 


& 


possible.  ^  The  writer  has  no  a  priori  objection  to  this 
suggestion  which  agrees  with  earlier  observations  by 
Morgan  except  that  it  is  at  present  difficult  to  harmonize 
it  with  all  the  facts.  Why  should  it  be  possible  to 
replace  the  treatment  with  the  hypertonic  solution  by 
a  suspension  of  the  oxidations  in  the  egg  for  three  hours 
while  we  know  that  lack  of  oxygen  suppresses  the  for- 
mation of  astrospheres  in  the  fertilized  eggs?  What 
becomes  of  the  astrospheres  if  the  treatment  with  the 
hypertonic  solution  precedes  the  membrane  formation 
by  a  number  of  hours  or  a  day  (which  is  possible  as 
we  shall  see),  and  why  do  they  not  induce  cell  division, 
if  Herlant's  idea  is  correct?  Nevertheless  the  sugges- 
tion of  Herlant  deserves  to  be  taken  into  serious  con- 
sideration. 

6.  How  can  an  alteration  of  the  surface  of  the  egg 
— e.  g.,  a  cytolytic  or  other  destruction  of  the  cortical 
layer — lead  to  a  beginning  of  development?  The 
answer  is  possibly  given  in  the  relation  of  oxidation  to 
development.  The  writer  found  in  1895  that  if  oxygen 
is  withdrawn  from  the  fertilized  sea-urchin  egg  it  can 
not  segment  and  this  seems  to  be  the  case  for  eggs  in 
general.^  In  1906  he  found  that  the  rapid  disintegra- 
tion of  the  eggs  of  the  sea  urchin  which  follows  artificial 

'  It  is  also  important  to  remember  that  the  formation  of  astrospheres 
after  mere  membrane  formation  occurs  considerably  more  slowly  than 
if  the  egg  has  also  received  a  treatment  with  a  hypertonic  solution. 

^  The  writer  found  that  the  e^gs  of  Fundulus  will  segment  a  number 
of  times  even  if  all  the  oxygen  has  apparently  been  removed. 


Artificial  Parthenogenesis  117 

membrane  formation  could  be  prevented  when  the 
eggs  were  deprived  of  oxygen  or  when  the  oxidations 
were  suppressed  in  the  eggs  by  KCN.  This  suggested 
a  connection  between  the  disintegration  of  the  egg 
after  artificial  membrane  formation  and  the  increase 
in  the  rate  of  oxidations ;  and  he  found  further  that  the 
formation  of  acid  is  greater  in  the  fertilized  than  in  the 
unfertilized  egg.  He,  therefore,  expressed  the  view 
in  1906  that  the  essential  feature  (or  possibly  one  of  the 
essential  features)  of  the  process  of  fertilization  was 
the  increase  of  the  rate  of  oxidations  in  the  egg  and 
that  this  increase  was  caused  by  the  membrane  forma- 
tion alone.  ^  These  conclusions  have  been  since  amply 
confirmed  by  the  measurements  of  0.  Warburg  as 
well  as  those  of  Loeb  and  Wasteneys,  both  showing  that 
the  entrance  of  the  spermatozoon  into  the  egg  raises 
the  rate  of  oxidations  from  400  to  600  per  cent.,  and  that 
membrane  formation  alone  brings  about  an  increase 
of  similar  magnitude.  Loeb  and  Wasteneys  found 
that  the  hypertonic  solution  does  not  increase  the  rate 
of  oxidations  in  a  fertilized  egg.  It  does  do  so,  how- 
ever, in  an  unfertilized  egg  without  membrane  forma- 
tion, but  merely  for  the  reason  that  in  such  an  egg  the 
hypertonic  solution  brings  about  the  cytolytic  change  in 
the  cortex  of  the  egg  underlying  membrane  formation.  ^ 

*  Loeb,  J.,  Biochem.  Ztschr.,  1906,  ii.,  183. 

"  Thus  the  treatment  of  an  unfertilized  egg  without  membrane  with 
a  hypertonic  solution  combines  two  effects,  first  the  general  cytolytic 


ii8  Artificial  Parthenogenesis 

According  to  Warburg  it  is  probable  that  the  oxi- 
dations occur  mainly  if  not  exclusively  at  the  surface 
of  the  egg  since  NaOH,  which  does  not  diffuse  into  the 
egg,  raises  the  rate  of  oxidations  more  than  NH4OH 
which  does  diffuse  into  the  egg.  And  finally,  the  same 
author  showed  that  the  oxidations  in  the  sea-urchin 
egg  are  due  to  a  catalytic  process  in  which  iron  acts 
as  a  catalyzer.^  In  view  of  all  these  facts  and  their 
harmony  with  the  methods  of  artificial  parthenogenesis 
the  suggestion  is  justifiable  that  the  alteration  or 
cytolysis  of  the  cortical  layer  of  the  egg  is  in  some 
way  connected  with  the  increased  rate  of  oxidations. 
The  question  remains  then:  How  can  membrane  for- 
mation or  the  alteration  of  the  cortical  layer  underlying 
membrane  formation  cause  an  increase  in  the  rate  of  oxi- 
dations? One  possibility  is  that  the  iron  (or  whatever 
the  nature  of  the  catalyzer  may  be)  exists  in  the  cortex 
of  the  egg  in  a  masked  condition — or  in  a  condition  in 
which  it  is  not  able  to  act — while  the  alteration  of  the 
cortical  layer  makes  the  iron  active.  It  might  be  that 
either  the  iron  or  the  oxidizable  substrate  is  contained 
in  the  lipoid  layer  in  the  unfertilized  condition  of  the  egg 
and  that  the  destruction  or  cytolysis  of  the  cortical 
layer  brings  both  the  iron  and  the  oxidizable  substrate 
into  the  watery  phase  in  which  they  can  Interact. 

alteration  of  the  cortical  layer  of  the  membrane  and  the  corrective 
effect  of  the  hypertonic  solution.  The  former  effect  raises  the  rate  of 
oxidations  in  the  egg,  the  latter  does  not. 

'  Warburg,  O.,  Sitzngsber.  d.  Heidelberger  Akad.  d.  Wissnsch.,  B.  1914. 


Artificial  Parthenogenesis  119 

Another  possibility  is  that  the  act  of  fertilization  in- 
creases the  permeability  of  the  egg.  This  idea,  which 
seems  attractive,  was  first  suggested  and  discussed 
by  the  writer  in  1906.^  He  had  found  that  when 
fertilized  and  unfertilized  eggs  were  put  into  ab- 
normal salt  solutions,  e.  g.,  pure  solutions  of  NaCl, 
the  fertilized  eggs  died  more  rapidly  than  the  unfer- 
tilized eggs  and  he  pointed  out  that  these  experiments 
suggested  the  possibility  that  fertilization  increases 
the  permeability  of  the  egg  for  salts.  The  reason  for 
his  hesitation  to  accept  this  interpretation  was,  that 
the  fertilized  ^<gg  is  also  more  easily  injured  by  lack 
of  oxygen  than  the  unfertilized  egg  and  in  this  case 
the  greater  sensitiveness  of  the  fertihzed  Q%g  was  ob- 
viously due  to  its  greater  rate  of  metabolism.  Later 
experiments  by  the  writer  showed  that  the  fertilized 
egg  can  be  made  more  resistant  to  abnormal  salt  solu- 
tions if  its  development  is  suppressed  by  lack  of  oxygen 
or  by  KCN  or  by  certain  narcotics.  With  our  present 
knowledge  it  does  not  seem  very  probable  that  lack 
of  oxygen  diminishes  the  permeability  of  the  ^g^,  but 
we  know  that  it  inhibits  the  developmental  processes. 
Warburg  has  made  it  appear  very  probable  that  the 
fertilized  egg  is  impermeable  for  NaOH  and  if  this  is 
the  case  it  should  also  be  impermeable  for  NaCl.  ^ 

'  Loeb,  J.,  Biochem.  Ztschr.,  1906,  ii.,  87. 

^  Unless  the  egg  is  left  so  long  in  the  pure  NaCl  solution  that  its 
permeability  is  increased. 


120  Artificial  Parthenogenesis 

The  idea  that  fertiHzation  and  membrane  formation 
cause  an  increase  in  the  permeabiHty  of  the  egg  was 
later  accepted  and  elaborated  by  R.  Lilhe.  This 
author  assumes  that  the  unfertiHzed  egg  cannot  de- 
velop because  it  contains  too  much  CO  2  but  that  the 
CO  2  can  escape  from  the  egg  as  soon  as  its  permeability 
is  increased  through  the  destruction  of  the  cortical 
layer  of  the  egg.^  After  the  CO  2  has  escaped,  the 
excessive  permeability  must  be  restored  to  its  normal 
value  and  this  is  the  role  of  the  hypertonic  treatment. 
It  is,  however,  difficult  to  harmonize  the  assumption 
of  an  impermeability  of  the  unfertilized  egg  for  CO  2 
with  the  fact  that  if  the  unfertilized  sea-urchin  egg  is 
cut  into  two,  as  is  done  in  merogony,  no  development 
takes  place,  while  such  pieces  will  develop  when  a 
spermatozoon  enters.  The  cortical  layer  is  removed 
along  the  cut  surface  and  there  is  no  reason  why  the 
CO  2  should  not  escape.  Besides,  the  experiments  of 
Godlewski  and  the  writer  prove  that  the  cortical  layer 
of  the  unfertilized  sea-urchin  egg  is  apparently  very 
permeable  for  CO  2  since  the  latter  causes  membrane 
formation  if  contained  in  the  sea  water  in  sufficiently 
high  concentration. 

Lillie  assumes  that  the  hypertonic  treatment  restores 
the  permeability  raised  to  excess  by  the  butyric  acid 
treatment,  but  this  assumption  is  not  in  harmony  with 

'Lillie,  R.  S.,  Jour.  MorphoL,  1911,  xxii.,  695;  Am.  Jour.  Physiol., 
191 1,  xxvii.,  289. 


Artificial  Parthenogenesis  121 

the  following  facts.  The  writer  has  shown  that  it  is 
immaterial  whether  the  eggs  are  treated,  first  with  the 
hypertonic  solution  and  then  with  butyric  acid  or  the 
reverse,  if  only  the  eggs  remain  longer  in  the  hypertonic 
solution  when  the  hypertonic  treatment  precedes  the 
butyric  acid  treatment.  It  was  stated  in  the  beginning 
of  this  chapter  that  the  development  of  the  egg  can 
be  induced  by  hypertonic  sea  water,  and  we  know  the 
reason  since  hypertonic  sea  water  is  a  cytolytic  agency. 
The  writer  found  that  when  we  expose  unfertilized 
eggs  of  purpuratus  for  from  two  to  two  and  a  half- 
hours  to  hypertonic  sea  water  they  will  often  not  de- 
velop and  only  a  few  eggs  will  undergo  the  first  cell 
divisions,  then  going  into  a  condition  of  rest.  When 
these  eggs,  both  the  segmented  and  unsegmented,  were 
treated  twenty-four  or  thirty-six  hours  later  with 
butyric  acid,  so  that  they  formed  a  membrane,  they 
all  developed  into  larvs  without  further  treatment. 
It  is  impossible  to  apply  Lillie's  theor}^  to  these  facts, 
for  the  simple  reason  that  the  treatment  with  hyper- 
tonic sea  water  was  just  long  enough  to  induce  de- 
velopment in  some  eggs  and  hence  according  to  LilHe's 
ideas  must  have  increased  the  permeability  of  these 
eggs.  Yet  these  same  eggs  were  induced  to  develop 
normally  when  subsequently  treated  with  butyric 
acid,  which  according  to  LiUie  also  acts  by  increasing 
the  permeability.  Nothing  indicates  that  the  treat- 
ment of  the  eggs  with  a  hypertonic  solution  diminishes 


122  Artificial  Partlieno<T:enesis 


fc. 


their  permeability;  the  reverse  would  be  much  more 
probable. 

Lillie's  theory  also  fails  to  explain  that  mere  treat- 
ment of  the  eggs  with  a  hypertonic  solution  can  bring 
about  their  development  into  larvae.  This,  however, 
is  intelligible  on  the  assumption  that  the  hypertonic 
solution  in  this  case  has  two  different  effects,  first  a 
cytolysis  of  the  cortical  layer  of  the  egg  and  second  an 
entirely  different  effect,  possibly  upon  the  interior  of 
the  egg,  which  represents  the  second  or  corrective  effect. 

McClendon'  has  shown  that  the  electrical  conduc- 
tivity of  the  egg  is  increased  after  fertilization,  and  J. 
Gray^  has  found  that  this  increase  in  conductivity  is 
only  transitory  and  disappears  in  fifteen  minutes. 
This  might  indicate  that  the  egg  becomes  transitorily 
more  permeable  for  salts  after  the  entrance  of  the 
spermatozoon  or  after  membrane  formation;  although 
an  increase  in  conductivity  might  be  caused  by  other 
changes  than  a  mere  increase  in  permeability  of  the 
egg.  The  writer  is  of  the  opinion  that  it  is  necessary 
to  meet  all  these  and  other  difficulties  before  we  can 
state  that  the  alteration  of  the  cortical  layer,  which  is 
the  essential  feature  of  development,  acts  chiefly  or  ex- 
clusively by  an  increase  in  the  permeability  of  the  egg.  ^ 

'  McClendon,  J.  P.,  Publications  of  the  Carnegie  Institution,  No.  183, 
125;  Am.  Jour.  Physiol.,  1910,  xxvii.,  240. 

'Gray,  J.,  Proc.  Cambridge  Philosophical  Society,  19 13,  xvii.,  i. 

3R.  Lillie  has  recently  shown  that  in  a  hypotonic  solution  water 
di.Tuses  more  rapidly  into  a  fertilized  than  into  an  unfertilized  egg. 


Artificial  Parthenogenesis  123 

/ 

7.  When  the  experiments  on  artificial  partheno- 
genesis were  first  pubHshed  they  aroused  a  good  deal 
of  antagonism  not  only  among  reactionaries  in  general 
but  also  among  a  certain  group  of  biologists.  O. 
Hertwig  had  defined  fertilization  as  consisting  in  the 
fusion  of  two  nuclei,  the  egg  nucleus  and  the  sperm 
nucleus.  No  such  fusion  of  two  nuclei  takes  place  in 
artificial  parthenogenesis  since  no  spermatozoon  enters 
the  egg,  and  it  became  necessary,  therefore,  to  abandon 
Hertwig's  definition  as  wrong.  The  objection  raised 
that  the  phenomena  are  limited  to  a  few  species  soon 
became  untenable  since  it  has  been  possible  to  produce 
artificial  parthenogenesis  in  the  egg  of  plants  {Fucus, 
according  to  Overton)  as  well  as  of  animals,  from  echino- 
derms  up  to  the  frog;  and  it  may  possibly  one  day  be 
accomplished  also  in  warm-blooded  animals.  A  second 
objection  was  that  the  eggs  caused  to  develop  by  the 
methods  of  artificial  parthenogenesis  could  never  reach 
the  adult  stage  and  that  hence  the  phenomenon  was 
merely  pathological.  There  was  no  basis  for  such  a 
statement,  except  that  it  is  extremely  difficult  to  raise 
marine  invertebrates.     Delage^  was  courageous  enough 


This  is  exactly  what  one  should  expect  since  the  unfertilized  egg  is  not 
only  surrounded  by  the  cortical  layer  but  also  by  a  thick  layer  of  jelly 
both  of  which  are  lacking  in  the  fertilized  egg.  It  is  difficult  to  under- 
stand how  this  observation  can  throw  any  light  on  the  mechanism  of 
development,  since  water  diffuses  rapidly  enough  into  the  unfertilized 
egg. 

'  Delage,  Y.,  Cotnpt.  rend.  Acad.  Sc,  1909,  cxlviii.,  453. 


124  Artificial  Parthenogenesis 

to  make  an  attempt  to  raise  parthenogenetic  larvae  of 
the  sea  urchin  beyond  the  larval  stage  and  he  succeeded 
in  one  case  in  carrying  the  animal  to  the  mature  stage. 
It  proved  to  be  a  male. 

Better  opportunities  were  offered  when  a  method  was 
discovered  which  induced  the  development  of  the  un- 
fertilized eggs  of  the  frog.  In  1907,  Guyer  made  the 
surprising  observation  that  if  he  injected  lymph  or 
blood  into  the  unfertilized  eggs  of  frogs  he  succeeded 
in  starting  development  and  he  even  obtained  two 
free-swimming  tadpoles.  ' '  Apparently  the  white  rather 
than  the  red  corpuscles  are  the  stimulating  agents 
which  bring  about  development,  because  injections  of 
lymph  which  contains  only  white  corpuscles  produce 
the  same  effects  as  injections  of  blood."  Curiously 
enough,  Guyer  thought  that  probably  the  cells  which 
he  introduced  and  not  the  egg  were  developing.  In 
19 10,  Bataillon  showed  that  a  mere  puncture  of  the 
egg  with  a  needle  could  induce  development  but  he 
believes  that  for  the  full  development  the  introduction 
of  a  fragment  of  a  leucocyte  is  required.  Bataillon 
has  called  attention  to  the  analogy  with  the  writer's 
results  on  lower  forms,  the  puncturing  of  the  egg 
corresponding  to  the  cytolysis  of  the  surface  layer  of  the 
egg  and  the  introduction  of  a  leucocyte  as  the  analogue 
of  the  second  or  corrective  factor.  The  method  of 
producing  artificial  parthenogenesis  by  puncturing 
the  egg  has  thus  far  been  successful  only  in  the  egg  of 


Fig.  6. 


Artificial  Parthenogenesis  125 

the  frog.  The  writer  has  tried  it  in  vain  on  the  eggs 
of  many  other  forms.  He  has  at  present  seven  par- 
thenogenetic  frogs  over  a  year  old,  produced  by  merely 
puncturing  the  eggs  with  a  fine  needle  (Fig.  6). 
These  frogs  have  reached  over  half  the  size  of  the  adult 
frog.  They  can  in  no  way  be  distinguished  from  the 
frogs  produced  by  fertilization  with  a  spermatozoon. 
This  makes  the  proof  conclusive  that  the  methods  of 
artificial  parthenogenesis  can  result  in  the  production 
of  normal  organisms  which  can  reach  the  adult  stage. 

Bancroft  and  the  writer  tried  to  determine  the  sex 
of  a  parthenogenetic  tadpole  and  of  a  frog  just  carried 
through  metamorphosis.  Since  in  early  life  the  sex 
glands  of  both  sexes  in  the  frog  contain  eggs  it  is  not 
quite  easy  to  determine  the  sex,  except  that  in  the  male 
the  eggs  gradually  disappear  and  from  this  and  other 
criteria  we  came  to  the  conclusion  that  both  partheno- 
genetic specimens,  which  were  four  months  old,  were 
males. 

The  writer  has  recently  examined  the  gonads  of  a 
ten  months  old  parthenogenetic  frog.  Here  no  doubt 
concerning  the  sex  was  possible  since  the  gonads  were 
well-developed  testicles  containing  a  large  number  of 
spermatozoaof  normal  appearance,and  no  eggs.  ^  (Figs. 
7  and  8.)  This  would  indicate  that  the  frog  belongs  to 
those  animals  in  which  the  male  is  heterozygous  for  sex. 

^  Since  this  was  written,  two  more  of  the  parthenogenetic  frogs  over 
a  year  old  died.     Both  were  males. 


126  Artificial  Parthenogenesis 

a.  The  fact  that  the  egg  of  so  high  a  form  as  the 
frog  can  be  made  to  develop  into  a  perfect  and  normal 
animal  without  a  spermatozoon — although  normally 
the  egg  of  this  form  does  not  develop  unless  a  sperma- 
tozoon enters — corroborates  the  idea  expressed  in 
previous  chapters  that  the  egg  is  the  future  embryo 
and  animal;  and  that  the  spermatozoon,  aside  from  its 
activating  effect,  only  transmits  Mendelian  characters 
to  the  egg.  The  question  arises :  Is  it  possible  to  cause 
a  spermatozoon  to  develop  into  an  embryo?  The  idea 
has  been  expressed  that  the  egg  was  only  the  nutritive 
medium  on  which  the  spermatozoon  developed  into 
an  embryo,  but  this  idea  has  been  rendered  untenable 
by  the  experiments  on  artificial  parthenogenesis.  Never- 
theless the  question  whether  or  not  the  spermatozoon 
can  develop  into  an  embryo  on  a  suitable  culture 
medium  remains,  and  it  can  only  be  decided  by  direct 
experiments.  It  was  shown  by  Boveri,  Morgan,  Delage, 
Godlewski,  and  others,  that  if  a  spermatozoon  enters 
an  enucleated  egg  or  piece  of  egg  it  can  develop  into 
an  embryo,  but  since  the  cytoplasm  of  the  Qg%  is  the 
future  embryo  this  experiment  proves  only  that  the 
egg  nucleus  may  be  replaced  by  the  sperm  nucleus; 
and  also  that  the  sperm  nucleus  carries  into  the  egg 
the  substances  which  induce  development.  Inciden- 
tally these  experiments  on  merogony  also  prove  that 
the  mere  mechanical  tearing  of  the  cortical  layer, — 
which  must  happen  in  the  separation  of  the  unfertilized 


•"  •■^•.  ^ .     •'•->v-  ?n?'  y*-    .r^ 


^%^° 


Fig.  7. 


Artificial  Parthenogenesis  127 

egg  into  parts  with  and  without  a  nucleus, — by  dissection 
or  by  shaking,  is  not  sufficient  to  start  development 
in  the  sea-urchin  egg. 

J.  de  Meyer  put  the  spermatozoa  of  sea  urchins 
into  sea  water  containing  an  extract  of  the  eggs  of  the 
same  species  but  found  only  that  the  spermatozoa 
swell  in  such  a  solution.  Loeb  and  Bancroft  made 
extensive  experiments  in  cultivating  spermatozoa  of 
fowl  in  vitro  on  suitable  culture  media.  In  yolk  and 
white  of  egg  the  head  of  the  spermatozoon  underwent 
transformation  into  a  nucleus,  but  no  mitosis  or  aster 
formation  was  observed.'  These  experiments  should 
be  continued. 

*  Loeb,  J.,  Artificial  Parthenogenesis  and  Fertilization,  Chicago,  1913. 


CHAPTER  VI 

DETERMINISM    IN    THE    FORMATION    OF    AN    ORGANISM 
FROM   AN    EGG 

I.  The  writer  in  a  former  book  {Dynamics  of  Living 
Matter,  1906,  p.  i),  defined  living  organisms  as  chemical 
machines  consisting  chiefly  of  colloidal  material  and 
possessing  the  peculiarity  of  preserving  and  reproducing 
themselves.  Some  authors  like  Driesch,  and  v.  Uex- 
kiill  seem  to  find  it  impossible  to  account  for  the  devel- 
opment of  such  machines  from  an  undifferentiated  egg 
on  a  purely  physicochemical  basis.  A  study  of  Driesch's 
very  interesting  and  important  book^  shows  that  he 
assumes  the  eggs  of  certain  animals,  e.  g.,  the  sea  urchin, 
to  consist  of  homogeneous  material;  and  he  concludes 
that  nature  has  solved,  in  the  formation  of  highly  differ- 
entiated organisms  from  such  undifferentiated  material, 
a  problem  wliich  does  not  seem  capable  of  a  solution 
by  physicochemical  agencies  alone.  But  the  supposi- 
tion of  a  structureless  egg  is  wrong,  since  Boveri  has 

*  Driesch,  H.,  Science  and  Philosophy  oj  the  Organism.  London, 
1908  and  1909. 

Z28 


Organisms  from  Eggs  129 

demonstrated  the  existence  of  a  very  simple  but  definite 
structure  in  the  unfertilized  egg  of  the  sea  urchin;  and 
a  similar  simple  structure  has  been  demonstrated  by- 
other  authors,  especially  Conklin,  in  the  eggs  of  other 
forms. 

In  this  chapter  we  shall  attempt  the  task  among 
others  of  showing  how,  on  the  basis  of  the  simple  physi- 
cochemical  structure  of  the  unfertilized  egg,  the  main 
organ  of  self-preservation  of  the  organism,  the  intestine, 
is  formed  through  the  mere  process  of  cell  division  and 
growth.  Cell  division  is  the  most  general  of  the  specific 
functions  of  Hving  matter  and  it  is  the  basis  underlying 
the  differentiation  of  the  comparatively  simple  struc- 
ture of  the  egg  into  a  more  complex  organism.  If  cell 
division  and  growth  were  equal  in  all  parts  of  the  egg 
no  differentiation  would  be  possible,  but  the  different 
regions  of  the  unfertilized  egg  contain  different  consti- 
tuents and  these,  probably  on  account  of  their  chemical 
difference,  do  not  all  begin  to  grow  or  divide  simulta- 
neously and  equally. 

Boveri^  found  that  in  the  unfertilized  egg  of  the  sea 
urchin  Strongylocentrotus  lividus  at  Naples  a  definite 
structure  is  indicated  by  the  fact  that  the  yellowish-red 
pigment  is  not  equally  distributed  over  the  whole 
surface  of  the  egg  but  is  arranged  in  a  wide  ring  from 
the  equator  almost  to  one  of  the  poles.     Thus  three 

^Boveri,  Tiu,  Verhandl.  d.  pkysik.-med.  Gesellsch.,  Wurzburg,  1901, 
xxxiv.,  145. 
9 


I30 


Organisms  from  Eggs 


zones  can  be  recognized  in  the  egg  (Fig.  9),  a  small  clear 
cap   A    at  one   pole,    a   pigmented   ring   B,  and   the 

rest  again  un- 
pigmented  C. 
Observation 
has  shown  that 
each  one  of 
these  regions 
gives  rise  to  a 
definite  con- 
stituent of 
the  egg :  A  f ur- 
nishes  the 
mesenchyme 
from  which  the 
skeleton  and 
the  connective  tissue  originate;  B  is  the  material  for 
the  formation  of  the  intestine,  and  C  gives  rise  to  the 
ectoderm. 

The  pigment  is  only  at  the  surface  of  the  egg,  and  its 
collection  at  B  indicates  only  that  the  material  in  B 
differs  physicochemically  from  A  and  C.  The  real 
determiners  of  the  three  different  groups  of  organs  are 
three  different  groups  of  substances  whose  distribution 
is  approximately  but  probably  not  wholly  identical 
with  the  regions  indicated  by  distribution  of  pigment. 
The  intestine-forming  material  is  probably  not  entirely 
lacking  in  C  but  is  contained  here  in  a  lower  concen- 


FiG.  9 


Organisms  from  Eggs 


131 


Fig.  10 


tration  and  probably  the  more  so  the  greater  the  dis- 
tance from  B;  and  the  same  m.ay  probably  be  said  for 
the  substances  determin- 
ing mesenchyme  and 
ectoderm  formation. 
Hence  the  unfertilized 
egg  contains  already  a 
rough  preformation  of 
the  embr^^o  inasmuch  as 
the  main  axis  of  the  em- 
bryo and  the  arrange- 
ment of  its  first  organs 
are  determined. 

After  the  egg  is  fertilized  the  cell  divisions  begin. 
The  first  division  is  as  a  rule  at  right  angles  to  the 

stratification  of  the 
egg,  each  of  the  two 
cells  contains  one-half 
of  the  pigment  ring 
(and  of  each  of  A  and 
C)  (Fig.  10),  and  after 
the  next  division  each 
contains  one-fourth  of 
the  pigmented  part. 
Each  of  the  four  cells 
is  a  diminutive  whole 
egg  since  each  contains 
the  three  layers  in  the  normal  arrangement  (Fig.  11). 


Fig.  II 


132 


Organisms  from  Eggs 


Fig.  12 


The  next  divisions  bring  about  an  unequal  division 
of  the  material.     Four  cells  will  be  formed  of  ectoderm 

material  C  and  only- 
little  intestine  ma- 
terial B,  the  other 
four  cells  containing 
5andyl.  These  lat- 
ter form  at  the  next 
division  four  very- 
small  colourless 
cells,  the  so-called 
micromeres,  A  (Fig. 
12),  from  which  the 
mesenchyme,  skele- 
ton, and  connective  tissue  are  formed,  four  larger  cells, 

B,  from  which  the  intestine  is  formed,  and  eight  cells, 

C,  from  which  the  ectoderm  will  arise.  The  separa- 
tion of  the  three  groups  of  substances  is  probably-  not 
as  complete  as  our  purely  diagrammatic  drawing  (Fig. 
12)  indicates. 

The  cell  division  proceeds  and  the  cells  become  smaller 
and  smaller  and  all  gather  at  the  surface  of  the  egg, 
thus  forming  a  hollow  sphere.  It  is  not  known  what 
brings  about  this  gathering  of  the  cells  at  the  surface, 
whether  it  is  protoplasmic  creeping  or  streaming  or 
whether  the  cells  are  held  by  a  jelly-like  layer  which 
covers  the  surface  of  the  egg  (hyaline  membrane)  (Fig. 
13).     Then  the  cilia  are  formed  at  the  external  surface 


Organisms  from  Eggs 


133 


of  these  cells  and  the  egg  begins  to  swim ;  we  say  it  has 
reached  the  first  larval,  the  so-called  blastula  stage. 
This  happens  according 
to  Driesch  after  the 
tenth  series  of  cell  divi- 
sions, when  the  number 
of  cells  is  theoretically 
1024,  in  reality  not  quite 
so  many  (between  800 
and  900).  The  next  step 
consists  in  the  cells  de- 
rived from  the  material 
A  (mesenchyme  and  mi- 
cromeres)     gliding    into 

the  hollow  sphere,  where  they  form  a  ring,  the  physico- 
chemical  process  respon- 
sible for  this  gliding  being 
yet  unknown.  At  the 
opening  of  this  ring  an  ac- 
tive growing  of  the  cells 
of  the  entoderm  into  the 
hollow  sphere  takes  place 
and  the  hollow  cylinder 
formed  by  this  growth 
is  the  intestine  (Fig.  14). 
Why  the  cells  grow  into 


Fig.  13 


Fig.  14 


the  hollow  sphere  and  not  into  the  opposite  direction 
is   unknown.       The  next  step  is   the   formation  of  a 


134  Organisms  from  Eggs 

skeleton  by  the  formation  of  crystals  consisting  of  the 
CaCOjby  the  mesenchyme  cells  surrounding  the  intes- 
tine. For  the  establishment  of  the  principle  in  which 
we  are  interested  the  description  of  morphogenesis 
need  not  be  carried  farther. 

This  principle  which  is  under  discussion  here  is  the 
development  of  a  purposeful  arrangement  of  organs 
out  of  the  egg.  If  we  assume  that  the  egg  consists 
of  homogeneous  material  we  are  indeed  confronted  with 
a  riddle.  Since  the  facts  contradict  such  an  assump- 
tion but  show,  as  Boveri  has  pointed  out,  a  prearrange- 
ment  which  allows  us  to  indicate  in  the  unfertilized 
egg  already  the  exact  spot  where  the  intestine  will  grow 
into  the  blastula  cavity,  we  are  on  solid  physicochemical 
ground,  although  many  questions  of  detail  cannot  yet 
be  answered.  Such  a  preformation  as  Boveri  has  de- 
monstrated is  only  conceivable  if  the  material  of  the 
egg  has  not  too  high  a  degree  of  fluidity;  we  may  con- 
sider it  as  consisting  essentially  of  a  semi-solid  gel 
which  is  not  homogeneous  throughout  the  egg  but 
divided  into  three  strata. 

2.  Lyon'  tried  to  ascertain  whether  by  centrifuging 
the  sea-urchin  egg  it  was  possible  to  modify  its  struc- 
ture and  thereby  affect  the  later  embryo.  He  and 
subsequent  experimenters  found  that  it  only  is  pos- 

'  Lyon,  E.  P.,  Arch.  f.  Entwcklngsmech.,  1907,  xxiii.,  151;  Morgan, 
T.  H.,  and  Spooner,  G.  B.,  ibid.,  1909,  xxviii.,  104;  Morgan,  Jour. 
Exper.  ZooL,  1910,  ix.,  594;  Conklin,  E.  G.,  ibid.,  1910,  ix.,  417;  Lillie, 
F.  R.,  Biol.  Bull.,  1909,  xvi.,  54. 


Organisms  from  Eggs  135 

sible  to  change  the  position  of  the  nucleus  and  the 
distribution  of  the  pigment  in  the  egg.  It  follows  from 
this  that  the  nucleus  and  the  pigment  are  suspended 
in  rather  fluid  material,  the  former  in  the  centre,  the 
pigment  at  or  near  the  surface.  The  position  of  the 
nucleus  determines  the  first  plane  of  segmentation, 
since  the  nuclear  division  precedes  the  division  of  the 
cytoplasm  of  the  egg  and  the  plane  of  nuclear  division 
becomes  also  the  plane  of  the  division  of  the  whole  egg 
— a  point  which  need  not  be  discussed  here.  It  was 
found,  however,  by  Lyon  and  the  subsequent  investi- 
gators that  the  place  where  the  micromeres  are  formed 
and  where  the  intestine  of  the  embryo  later  originates 
is  little  influenced  by  the  centrifuging  of  the  egg.  The 
localization  of  this  spot  must  therefore  be  determined 
by  a  structure  sufficiently  solid  not  to  be  shifted  by  the 
centrifugal  force.  The  intestinal  stratum  in  the  egg 
contains  the  forerunners  of  the  tissues  which  secrete  hy- 
drolyzing  enzymes,  e.  g.,  trypsin  into  the  digestive  tract. 
When  the  surrounding  solution  is  altered  in  consti- 
tution or  when  the  temperature  is  too  high,  the  intestine 
instead  of  growing  into  the  hollow  sphere  grows  outside, 
we  get  an  evagination  instead  of  an  invagination  of  the 
intestine.  Such  larvse  may  live  for  a  few  days  but  they 
cannot  grow  into  a  living  organism.  The  forces  which 
make  the  intestine  grow  into  the  hollow  sphere  are 
unknown ;  it  may  possibly  be  only  the  difference  between 
the  tension  on  the  external  and  internal  surfaces  of  the 


136  Organisms  from  Eggs 

hollow  sphere;  under  normal  conditions,  the  resistance 
on  the  inner  surface  being  smaller,  the  intestine  grows 
into  the  hollow  sphere. 

The  intestine  is  one  of  the  organs  required  for  the 
self-preservation  of  a  more  complicated  organism,  in 
fact  a  higher  organism  without  a  digestive  tract  is  not 
capable  of  living  for  any  length  of  time.  In  the  gastrula 
— i.  e.,  the  blastula  with  an  intestine — we  have  an 
organism  which  is  durable,  but  the  processes  leading  up 
to  the  formation  of  the  intestine  are  so  simple  that  it 
is  difficult  to  understand  why  the  assumption  of  a 
"supergene"  should  be  required  in  this  case. 

3.  Driesch^  was  the  first  to  show  that  if  we  isolate 
one  of  the  first  two  cells  of  a  dividing  egg  each  develops 
into  a  whole  embryo  of  half  size.  This  is  perfectly 
intelligible,  since  each  of  the  two  cells  contains  all  the 
three  layers  in  the  normal  arrangement  (Fig.  10).  The 
cells  divide  and  the  cells  having  the  tendency  to  creep 
to  the  surface  of  the  mass  arrange  themselves  in  a  hollow 
sphere,  the  blastula.  Since  micromeres  and  intestine 
material  are  present  and  in  their  normal  position  an 
intestine  will  grow  into  the  blastula  and  a  whole  or- 
ganism will  result.  All  of  this  is  as  necessary  as  is  the 
formation  of  one  embryo  from  the  whole  egg  material. 
Yet  the  two  half-embryos  betray  their  origin  from  two 
cleavage  cells  of  the  same  egg,  in  that  the  two  gastrulae 
formed  are  often  if    not  always  symmetrical  to  each 

» Driesch,  H.,  Ztschr.  f.  wissnsch.  ZooL,  1891,  liii.,  160. 


Organisms  from  Eggs 


137 


Fig.  15 


other  (Fig.  15),  as  the  writer  had  a  chance  to  observe 
in  the  egg  of  Strongylocentrotus  purpuratus''  in  the  fol- 
lowing experiment.  The  eggs  of  the  sea  urchin  Strongy- 
locentrotus purpuratus  are  put  soon  after  fertilization 
into  solutions  which  differ  from  sea  water  in  two 
points ;  namely  that  they  are  neutral  or  very  faintly  acid 
(through  the  C  0  2 
absorbed  from  the 
air)  instead  of  being 
faintly  alkaline,  and 
second,  that_  one  of 
the  following  three 
constituents  of  the 
sea  water  is  lacking; 
namely:  K,  Na,  or  Ca,  When  the  eggs  are  allowed  to 
segment  in  such  a  solution  the  first  two  cleavage  cells 
are  as  a  rule  in  a  large  percentage  of  cases — often  as 
many  as  ninety  per  cent. — separated  from  each  other, 
and  when  the  eggs  are  put  into  normal  sea  water  (about 
twenty  minutes  after  the  cell  division)  each  cell  develops 
into  a  normal  embryo.  In  a  number  of  cases  the  em- 
bryos remained  inside  the  egg  membrane  and  did  not 
move  until  after  the  invagination  of  the  intestine  was 
far  advanced;  in  such  cases  it  was  found  quite  often 
that  the  invagination  began  at  the  plane  of  cleavage  at 
symmetrical  points  of  the  two  embryos,  and  the  growth 
of  the  intestine  was  symmetrical  in  both  embryos. 

'  Loeb,  J.,  Arch.  f.  Entwcklngsmech.,  1909,  xxvii.,  119. 


138  Organisms  from  Eggs 

This  symmetry  is  probably  due  to  the  following  fact : 
the  first  cleavage  plane  goes  through  that  spot  where 
the  intestine  grows  into  the  blastula  cavity.  If  the 
micromere  material  does  not  change  its  position  after 
the  two  cleavage  cells  are  separated  and  the  new  blas- 
tulae  do  not  become  completely  spherical  the  symmetry 
which  we  observed  is  bound  to  occur.  The  occurrence 
is  a  confirmation  of  Boveri's  observation.  It  is  natural 
that  Driesch  also  found  that  each  cell  in  the  four-cell 
stage  should  give  rise  to  a  full  embryo,  since  each  of  these 
cells  is  in  reaHty  a  diminutive  egg  containing  the  three 
strata  in  the  right  arrangement.  When,  however,  the 
cells  of  the  eight-  or  sixteen-cell  stage  were  isolated 
Driesch's  results  were  different.  In  this  case  the  isolated 
cells  from  the  ectoderm  material  did  no  longer  all  form 
a  gastrula;  when  such  a  cell  still  formed  a  gastrula  it 
was  probably  due  to  the  fact  that  it  contained  some 
entoderm  material;  while  the  cells  taken  from  the 
entoderm  region  all  formed  embryos  and  therefore 
contained  ectoderm  material. '  The  isolated  ectoderm 
cells  of  a  blastula  could  no  longer  form  an  intestine; 
they  were  lacking  the  entoderm  material.  It  looks  as 
if  a  gradual  migration  of  all  the  entoderm  material 
from  the  ectoderm  into  the  entoderm  took  place  during 
the  blastula  formation. 

When  the  contents  of  the  egg  are  displaced  by  pres- 
sure the  result  will  be  determined  by  the  location  of 

»  Driesch,  H.,  Arch.  f.  Enlwcklngsmech.,  1900,  x.,  361. 


Organisms  from  Eggs  139 

the  main  mass  of  the  intestine-forming  material;  where 
the  main  mass  of  this  body  is  located  the  invagination 
of  the  intestine  will  take  place.  In  his  earlier  work 
Driesch  assumed  from  pressure  experiments  that  the 
egg  had  a  great  power  of  "regulation."  In  a  later 
paper  ^  he  expressed  to  a  large  extent  his  agreement 
with  Boveri  who  denied  this  power  of  "regulation"  and 
showed  that  the  existence  of  the  structure  of  the  egg — 
i.  e.,  a  division  into  three  strata,  one  forming  the  ecto- 
derm, the  second  the  entoderm,  and  the  third  the 
mesoderm — was  sufficient  to  explain  the  various  pheno- 
mena of  apparent  "regulation."  Driesch's  idea  of  a 
regulation  in  this  case  has  often  been  used  to  insist 
upon  the  non-explicability  of  the  phenomena  of  de- 
velopment from  a  purely  physicochemical  view-point. 
It  is,  therefore,  only  fair  to  point  out  that  Boveri^ 
has  furnished  the  facts  for  a  simpler  explanation,  which 
seems  to  have  escaped  the  notice  of  antimechanists.  ^ 

The  objection  may  be  raised  that  in  accepting  Boveri's 
facts  and  interpretation  we  pushed  the  miracle  only 
one  step  farther  and  that  we  now  have  to  explain  the 
origin  of  the  structure  in  the  unfertilized  egg.     This 

'  Driesch,  H.,  Arch.  f.  Entswcklngsmech.,  1902,  xiv.,  500. 

^  Boveri,  Th.,  Verhandl.  d.  physik.  med.  Gesellsch.,  Wurzburg,  N.F., 
1901,  xxxiv.,  145. 

3v.  UexkuU  makes  in  his  last  book  (Bausteine  zu  einer  biologischen 
Weltanschauung,  Munchen,  1913,  p.  24)  the  following  statement: 
"  Driesch  suceeded  in  showing  that  the  germ  cell  has  no  trace  of  a 
machine-like  structure  but  consists  entirely  of  equivalent  parts."  This 
is  not  correct. 


140  Organisms  from  Eggs 

Boveri  has  done  by  showing  that  the  egg  grows  from 
the  wall  of  the  ovary  and  that  that  part  of  the  egg 
which  is  connected  with  the  wall  of  the  ovary  gives 
rise  to  the  ectoderm  layer,  while  the  opposite  part  gives 
rise  to  the  mesenchyme  and  the  intestine.  This  shows 
a  connection  between  the  orientation  of  the  egg  in  the 
wall  of  the  ovary  and  its  stratification.  While  this 
does  not  solve  the  problem  of  stratification  in  the  egg 
it  gives  the  clue  to  its  solution. 

The  ultimate  origin  of  stratification  probably  goes 
back  to  the  fact  of  the  presence  of  watery  and  water- 
immiscible  substances,  such  as  fats.  The  experiments 
by  Beutner  and  the  writer  have  shown  that  the  electro- 
motive forces  which  are  observed  in  Uving  tissues 
originate  at  the  boundaries  between  a  watery  and  a  water- 
immiscible  phase,  like  oleic  acid  or  lecithin.^  In  his 
earlier  writings  ^  the  writer  had  thought  that  the  colloids 
had  special  significance  and  this  idea  seems  to  prevail 
today;  but  the  actual  observations  have  shown  that 
the  phase  boundary  fat-water  is  of  greater  importance. 
Needless  to  say  the  fats  if  not  present  in  the  cell 
from  the  beginning  can  be  formed  in  the  metabolism. 

4.  All  the  "regulation"  in  the  egg  is  of  a  purely 
physicochemical  character;  it  consists  essentially  of  a 
flow  of  material.     If  this  idea  is  correct,  the  apparent 

'  Loeb,  J.,  and  Beutner,  R.,  Biochem.  Zlschr.,  1912,  xli.,  i;  xliv.,  303; 
1913,  li.,  288;  li.,  300;  1914,  lix.,  195. 

'  Loeb,  J.,  The  Dynamics  of  Living  Matter.  New  York,  1906.  Intro- 
ductory Remarks. 


Organisms  from  Eggs  141 

power  of  "regulation"  of  the  blastomeres  should  differ 
according  to  the  degree  of  fluidity  and  the  possibility 
of  different  layers  separating,  and  this  assumption 
is  apparently  supported  by  facts.  The  first  plane  of 
segmentation  of  the  egg  is  usually  the  plane  of  sym- 
metry of  the  later  organism  and  where  the  degree  of 
fluidity  is  less  than  in  the  sea-urchin  egg,  a  separation 
of  the  two  first  blastomeres  should  easily  result  in  the 
formation  of  two  half-embryos  instead  of  two  whole 
embryos. 

This  is  the  case  for  the  frog's  egg  as  Roux  showed  in 
a  classical  experiment.  Roux  destroyed  one  of  the 
two  first  cleavage  cells  of  a  frog's  egg  with  a  hot  needle 
and  found  that  as  a  rule  the  surviving  cell  developed 
into  only  a  half-embryo.  ^  The  frog's  egg  consists  of 
two  substances,  a  lighter  one  which  is  on  top  and  a 
heavier  one  below.  Although  viscous,  the  two  sub- 
stances are  not  too  viscous  to  prevent  a  flow  if  the  egg 
is  turned  upside  down.  O.  Schultze  found  that  if  a 
normal  egg  is  turned  upside  down  in  the  two-cell  stage 
and  held  in  that  position,  two  full  embryos  arise,  one 
from  each  of  the  two  blastomeres.  Through  the  flow 
of  the  lighter  liquid  in  the  egg  upwards  the  two  halves 
of  the  protoplasm  on  top  become  separated  and  de- 
velop independently  into  two  whole  embryos  instead 
of  into  two  half-embryos.  In  Roux's  experiment  this 
flow  of  protoplasm  was  avoided.     Morgan  showed  that 

'Roux,  W.,  Virchow's  Archiv,  1888,  cxiv.,  113. 


142  Organisms  from  Eggs 

if  Roux's  experiment  is  repeated  with  the  modification 
that  the  egg  is  put  upside  down  after  the  destruction 
of  the  one  cell,  the  intact  cell  will  give  rise  not  to  a  half 
but  to  a  whole  embryo.^  These  experiments  prove 
that  each  of  the  first  two  cleavage  cells  of  the  frog's 
egg  represents  one-half  of  the  embryo  and  that  a  whole 
embryo  can  develop  from  each  half  only  when  a  re- 
distribution of  material  takes  place,  which  in  the  egg 
of  the  frog  can  be  brought  about  by  gravitation  since 
the  egg  consists  of  a  lighter  and  a  heavier  mass. 

When,  therefore,  in  the  egg  of  the  sea  urchin  each 
of  the  first  two  blastomeres  naturally  gives  rise  to  a 
whole  embryo  it  is  due  to  a  greater  degree  of  fluidity 
of  the  protoplasm  and  not  to  a  lack  of  preformation 
of  the  embryo  in  the  cytoplasm.  This  idea  is  confirmed 
by  the  observations  on  the  egg  of  Ctenophores  whose 
cytoplasm  seems  to  be  more  solid  than  that  of  most 
other  eggs.  Chun  found  that  the  isolated  blastomere 
of  the  first  cell  division  produced  a  half -larva,  possessing 
only  four  instead  of  the  eight  locomotor  plates  of  the 
normal  S.nimal. 

It  seems  that  in  the  egg  of  molluscs,  also,  the  simple 
symmetry  relations  of  the  body  are  already  preformed. 
It  is  well  known  that  there  are  shells  of  snails  which 
turn  to  the  right  while  others  turn  in  the  opposite 
direction.  The  shells  of  LymncBus  turn  to  the  right, 
those  of  Planorhis  to  the  left.     It  was  observed  by 

»  Morgan,  T.  H.,  Embryology  of  the  Frog.     New  York. 


Organisms  from  Eggs  143 

Crampton',  Kofoid,  and  Conklin  that  the  eggs  of 
right-wound  snails  do  not  segment  in  a  symmetrical, 
but  in  a  spiral,  order,  and  that  in  left-handed  snails 
the  direction  of  the  spiral  segmentation  is  the  reverse 
of  that  of  the  segmentation  in  the  right-handed  snails. 
Conklin  was  able  to  show  that  the  asymmetrical  spiral 
structure  is  already  preformed  in  the  egg  before  cleav- 
age. The  asymmetry  of  the  body  in  snails  is  therefore 
already  preformed  in  the  egg.^ 

E.  B.  Wilson^  has  found  a  marked  differentiation  in 
the  eggs  of  some  annelids  and  molluscs.  He  isolated 
the  first  two  blastomeres  of  the  egg  of  Lanice,  an  Anne- 
lid. These  two  blastomeres  are  somewhat  different 
in  size;  from  the  larger  one  of  the  first  two  blastomeres, 
the  segmented  trunk  of  the  worm  originates.  Wilson 
found  that 

when  either  cell  of  the  two-cell  stage  is  destroyed,  the  re- 
maining cell  segments  as  if  it  still  formed  a  part  of  an  entire 
embryo/  The  later  development  of  the  two  cells  differs 
in  an  essential  respect,  and  in  accordance  with  what  we 
should  expect  from  a  study  of  the  normal  development. 
The  posterior  cell  develops  into  a  segmented  larva  with  a 
prototroch,  an  asymmetrical  pre-trochal  or  head  region,  and 

*  Crampton,  H.  E.,  New  York  Academy  of  Sciences,  1894;  Kofoid, 
C.  A.,  Proc.  Am.  Acad.  Arts  a?td  Sciences,  1894,  xxix. 

^Conklin,  E.  G.,  Anat.  Anzeig.,  1903,  xxiii.,  577;  Heredity  and 
Environment  in  the  Development  of  Man.     Princeton,  1915,  p.  171. 

3  Wilson,  E.  B.,  Science,  1904,  xx.,  748;  Jour.  Exper.  ZooL,  1904,  i., 

I,  197- 

4 The  reader  will  notice  the  absence  of  "regulation." 


144  Organisms  from  Eggs 

a  nearly  typical  metameric  seta-bearing  trunk  region,  the 
active  movements  of  which  show  that  the  muscles  are 
normally  developed.  The  pre-trochal  or  head  region  bears 
an  apical  organ,  but  is  more  or  less  asymmetrical,  and,  in 
every  case  observed,  but  a  single  eye  was  present,  whereas 
the  normal  larva  has  two  symmetrically  placed  eyes.  The 
development  of  the  anterior  cell  contrasts  sharply  with  that 
of  the  posterior.  This  embryo  likewise  produces  a  proto- 
troch  and  a  pre-trochal  region,  with  an  apical  organ,  but 
produces  no  post-trochal  region,  develops  no  trunk  or  setae, 
and  does  not  become  metameric.  Except  for  the  presence 
of  an  apical  organ,  these  anterior  embryos  are  similar  in 
their  general  features  to  the  corresponding  ones  obtained 
in  Dentalium.  None  of  the  individuals  observed  developed 
a  definite  eye,  though  one  of  them  bore  a  somewhat  vague 
pigment  spot. 

This  result  shows  that  from  the  beginning  of  develop- 
ment the  material  for  the  trunk  region  is  mainly  localized 
in  the  posterior  cell;  and,  furthermore,  that  this  material 
is  essential  for  the  development  of  the  metameric  struc- 
ture. The  development  of  this  animal  is,  therefore,  to 
this  extent,  at  least,  a  mosaic  work  from  the  first  cleavage 
onward — a  result  that  is  exactly  parallel  to  that  which  I 
earlier  reached  in  Dentalium,  where  I  was  able  to  show  that 
the  posterior  cell  contains  the  material  for  the  mesoblast, 
the  foot,  and  the  shell;  while  the  anterior  cell  lacks  this 
material.  I  did  not  succeed  in  determining  whether,  as 
in  Dentalium,  this  early  localization  in  Lanice  pre-exists  in 
the  unsegmented  egg.  The  fact  that  the  larva  from  the 
posterior  cell  develops  but  a  single  eye,  suggests  the  possi- 
bility that  each  of  the  first  two  cells  may  be  already  specified 
for  the  formation  of  one  eye;  but  this  interpretation  remains 
doubtful  from  the  fact  that  the  larva  from  the  anterior 
cell  did  not,  in  the  five  or  six  cases  observed,  produce  any 
eye. 


Organisms  from  Eggs  145 

Conklin  has  established  the  existence  of  a  definite 
structure  in  the  unfertiHzed  eggs  of  Ascidians,  Amphi- 
oxus,  and  many  molluscs.  In  all  cases  the  results  of 
the  isolation  of  the  first  blastomeres  seem  to  agree  with 
the  demonstrable  structure  of  the  unfertilized  egg. 

5.  These  examples  may  suffice  to  show  that  the 
egg  has  from  the  beginning  a  simple  structure,  and 
we  will  now  point  out  by  which  means  further  differen- 
tiation may  come  about.  Sachs  suggested  that  all 
differentiation  and  the  formation  of  every  organ  pre- 
supposes the  previous  existence  of  specific  substances 
responsible  for  the  formation.  These  substances  which 
are  now  called  internal  secretions  or  hormones  develop 
gradually  during  embryonic  development.  What  ex- 
ists first  is  a  jelly-like  block  of  protoplasmic  material 
with  a  varying  degree  of  viscosity  and  with  just  enough 
differentiation  to  indicate  head  and  tail  end,  a  right 
and  left,  and  a  dorsal  and  ventral  side  of  the  future 
embryo. 

Aside  from  such  simple  differences  phenomena  of 
protoplasmic  streaming  contribute  to  the  further  differ- 
entiation. Such  streaming  begins,  according  to  Conk- 
lin, ^  in  the  egg  just  before  fertilization  when  the  surface 
layer  of  the  egg  protoplasm 

'  Conklin,  E.  G.,  Heredity  and  Environment  in  the  Development  of 
Man.  Princeton  University  Press,  1915.  The  reader  is  referred  to 
this  book  for  the  literature  and  main  facts  on  the  structure  of  the  egg; 
it  should  also  be  stated  that  Conklin's  book  is  one  of  the  best  introduc- 
tions to  modem  biology  in  the  English  literature. 


146  Organisms  from  Eggs 

streams  to  the  point  of  entrance  of  the  sperm,  and  these 
movements  may  lead  to  the  segregation  of  different  kinds 
of  plasma  in  different  parts  of  the  egg  and  to  the  unequal 
distribution  of  these  substances  in  different  regions  of  the 

egg. 

One  of  the  most  striking  cases  of  this  is  found  in  the 
Ascidian  Styela  in  which  there  are  four  or  five  different 
kinds  of  substances  in  the  egg  which  differ  in  colour,  so  that 
their  distribution  to  different  regions  of  the  egg  and  to 
different  cleavage  cells  may  be  easily  followed  and  even 
photographed  while  in  the  living  condition.  The  peripheral 
layer  of  protoplasm  is  yellow  and  when  it  gathers  at  the 
lower  pole  of  the  egg  where  the  sperm  enters  it  forms  a 
yellow  cap.  This  yellow  substance  then  moves  following 
the  sperm  nucleus,  up  to  the  equator  of  the  egg  on  the  poste- 
rior side  and  there  forms  a  yellow  crescent  extending  around 
the  posterior  side  of  the  egg  just  below  the  equator.  On 
the  anterior  side  of  the  egg  a  grey  crescent  is  formed  in  a 
somewhat  similar  manner  and  at  the  lower  pole  between 
these  two  crescents  is  a  slate-blue  substance,  while  at  the 
upper  pole  is  an  area  of  colourless  protoplasm.  The  yellow 
crescent  goes  into  cleavage  cells  which  become  muscle  and 
mesoderm,  the  grey  crescent  into  cells  which  become  ner- 
vous system  and  notochord,  the  slate-blue  substance  into 
endoderm  cells,  and  the  colourless  substance  into  ectoderm 
cells. 

Thus  within  a  few  minutes  after  the  fertilization  of  the 
egg  and  before  or  immediately  after  the  first  cleavage,  the 
anterior  and  posterior,  dorsal  and  ventral,  right  and  left 
poles  are  clearly  distinguishable,  and  the  substances  which 
will  give  rise  to  ectoderm,  endoderm,  mesoderm,  muscles, 
notochord,  and  nervous  system  are  plainly  visible  in  their 
characteristic  positions.^ 

'  Conklin,  E.  G.,  loc.  cit.,  p.  117. 


Organisms  from  Eggs  147 

We  may  finally  allude  briefly  to  the  fact  that  when 
once  a  number  of  tissues  are  difterentiated  each  one 
may  influence  the  other  by  calling  forth  tropistic  re- 
actions. Thus  the  writer  showed  that  in  the  yolk  sac 
of  the  fish  Fundulus  the  pigment  cells  lie  at  first  without 
any  definite  order  but  that  they  gradually  are  compelled 
to  creep  entirely  on  the  blood-vessels  and  form  a  sheath 
around  them  Vvdth  the  result  that  the  yolk  sac  assumes 
a  tiger-like  marking.^  Driesch^  has  pointed  out  that 
the  mesenchyme  cells  are  directed  in  their  migration; 
and  it  seems  that  the  direction  of  the  growth  of  the 
axis  cylinder  is  determined  by  the  tissues  into  which 
it  grows.  The  idea  of  tropistic  reactions  in  the  forma- 
tion of  organs  has  been  discussed  by  Herbst.^ 

6.  As  a  consequence  of  further  changes  definite 
anlagen  or  buds  originate  later  in  the  embr^'o  v.-hich 
are  destined  to  give  rise  to  definite  organs.  Thus  in 
the  tadpole  early  mesenchyme  cells  are  formed  which 
are  the  anlagen  for  the  four  legs,  which  will  grow  out 
under  the  proper  conditions.  These  anlagen  are 
specific  inasmuch  as  from  the  anlage  of  a  foreleg  only 
a  foreleg,  and  from  the  anlage  for  a  hindleg  only  a  hind- 
leg,  will  develop.     Braus"*  has  proved  this  by  trans- 

'  Loeb,  J.,  Jour.  Morphol.,  1893,  xiii.,  161;  Tlie  Mechanistic  Con- 
ception of  Life.     Chicago,  1912,  p.  106. 

'  Driesch,  H.,  Science  and  Philosophy  of  the  Organism,  i.,  p.  104. 

3  Herbst,  C,  Formative  Reize  in  der  tierischen  Ontogenese.  Leipzig, 
1901. 

^'Bra.us,!!.,  Miinchener  Med.  Wochnschr.,  1903,  i  (II.),  No.  47,  p. 
2076. 


148  Organisms  from  Eggs 

planting  the  anlage  of  a  foreleg  to  different  parts  of 
the  body.  No  matter  into  which  part  of  the  body  they 
are  transplanted  the  mesenchyme  cells  for  the  foreleg 
will  give  rise  to  a  foreleg  only;  even  if  they  are  trans- 
planted into  the  spot  from  which  the  hindlegs  grow  out 
under  natural  conditions.  There  is  therefore  nothing 
to  indicate  "regulation." 

The  same  is  true  for  the  formation  of  the  eye  and 
probably  in  general.  We  have  to  consider  the  forma- 
tion of  the  various  organs  of  the  body  as  being  due  to 
the  development  of  specific  cells  in  definite  locations 
in  the  organisms  which  will  grow  out  into  definite 
organs  no  matter  into  which  part  of  the  organism  they 
are  transplanted.  It  is  at  present  unknown  what 
determines  the  formation  of  these  specific  anlagen. 
They  may  lie  dormant  for  a  long  time  and  then  begin 
to  grow  at  definite  periods  of  development.  We  shall 
see  later  that  we  know  more  about  the  conditions  which 
cause  them  to  grow. 

7.  The  fact  that  the  egg,  and  probably  every  cell, 
has  a  definite  structure  should  determine  the  limits  of 
the  divisibility  of  living  matter.  In  most  cases  the 
complete  destruction  of  a  cell  means  the  cessation  of 
life  phenomena.  A  brain  or  kidney  which  has  been 
ground  to  a  pulp  is  no  longer  able  to  perform  its  func- 
tions; yet  we  know  that  such  pulps  can  still  perform 
some  of  the  characteristic  chemical  processes  of  the 
organ;  e.  g.,  the  alcoholic  fermentation  characteristic 


Organisms  from  Eggs  149 

of  yeast  can  be  caused  by  the  press  juice  from  yeast; 
or  characteristic  oxidations  can  be  induced  by  the 
ground  pulp  of  organs.  The  question  arises  as  to  how 
far  the  divisibiHty  of  Hving  matter  can  be  carried  with- 
out interfering  with  the  total  of  its  functions.  Are 
the  smallest  particles  of  living  matter  which  still  exhibit 
all  its  functions  of  the  order  of  magnitude  of  molecules 
and  atoms,  or  are  they  of  a  different  order?  The  first 
step  toward  obtaining  an  answer  to  this  question  was 
taken  by  Moritz  Nussbaum,^  who  found  that  if  an 
infusorian  be  divided  into  two  pieces,  one  with  and 
one  without  a  nucleus,  only  the  piece  with  a  nucleus 
will  continue  to  live  and  perform  all  the  functions  cf 
self-preservation  and  development  which  are  character- 
istic of  living  organisms.  This  shows  that  at  least  two 
different  structural  elements,  nucleus  and  cytoplasm, 
are  needed  for  life.  We  can  understand  to  a  certain 
extent  from  this  why  an  organ  after  being  reduced  to 
a  pulp,  in  which  the  differentiation  into  nucleus  and 
protoplasm  is  definitely  and  permanently  lost,  is  unable 
to  accomplish  all  its  functions.  ^ 

The  observations  of  Nussbaum  and  those  who  re- 
peated his  experiments  showed  that  although  two  differ- 
ent structures  are  required,  not  the  whole  mass  of  an 

'Nussbaum,  M.,  Arch.  f.  mikroscop.  Anat.,  1886,  xxvi.,  485. 

^  It  must  not  be  overlooked  that  in  bacteria  and  the  blue  algs  no 
distinct  differentiation  into  nucleus  and  protoplasm  can  be  shown.  To 
these  organisms,  therefore,  the  experiments  of  Nussbaum  cannot  be 
applied. 


150  Organisms  from  Eggs 

infusorian  is  needed  to  maintain  its  life.  The  question 
then  arose:  How  small  a  fraction  of  the  original  cell 
is  required  to  permit  the  full  maintenance  of  life  ?  The 
writer  tried  to  decide  this  question  in  the  egg  of  the 
sea  urchin.  He  had  found  a  simple  method  by  which 
the  eggs  of  the  sea  urchin  {Arbacia)  can  easily  be  divided 
into  smaller  fragments  immediately  after  fertilization. 
When  the  egg  is  brought  from  five  to  ten  minutes  after 
fertilization  (long  before  the  first  segmentation  occurs) 
into  sea  water  which  has  been  diluted  by  the  addition 
of  equal  parts  of  distilled  water,  the  egg  takes  up  water, 
swells,  and  causes  the  membrane  to  burst.  Part  of  the 
protoplasm  then  flows  out,  in  one  egg  more,  in  another 
less.  If  these  eggs  are  afterward  brought  back  into 
normal  sea  water  those  fragments  which  contain  a 
nucleus  begin  to  divide  and  develop.'  It  was  found 
that  the  degree  of  development  which  such  a  fragment 
reaches  is  a  function  of  its  mass;  the  smaller  the  piece, 
the  sooner  as  a  rule  its  development  ceases.  The  small- 
est fragment  which  is  capable  of  reaching  the  pluteus 
stage  possesses  the  mass  of  about  one-eighth  of  the 
whole  egg.  Boveri  has  since  stated  that  it  was  about 
one  twenty-seventh  of  the  whole  mass.  Inasmuch 
as  only  the  linear  dimensions  are  directly  measurable, 
a  slight  difference  in  measurement  will  cause  a  great 
discrepancy  in  the  calculation  of  the  mass.     Driesch's 

»  Loeb,  J.,  Arch.  d.  f.  ges.  Physiol.,  1893,  Iv.,  525. 


Organisms  from  Eggs  151 

results  disagree  with  the  statement  of  Boveri  and  support 
the  observation  of  the  writer. 

If  we  raise  the  question  w^hy  such  a  Hmit  exists  in 
regard  to  the  divisibihty  of  living  matter,  it  seems 
probable  that  only  those  fragments  of  an  egg  are 
capable  of  development  into  a  pluteus  which  contain  a 
sufficient  amount  of  material  of  each  of  the  three  layers. 
If  this  be  correct,  it  would  certainly  not  suffice  to  mix 
the  chemical  constituents  of  the  egg  in  order  to  produce 
a  normal  embryo ;  this  would  require  besides  the  proper 
chemical  substances  a  definite  arrangement  or  structure 
of  this  material.  The  limits  of  divisibility  of  a  cell 
seem  therefore  to  depend  upon  its  physical  structure 
and  must  for  this  reason  vary  for  different  organisms 
and  cells.  The  smallest  piece  of  a  sea-urchin  egg  that 
can  reach  the  pluteus  stage  is  still  visible  with  the  naked 
eye,  and  is  therefore  considerably  larger  than  bacteria 
or  many  algs,  which  also  may  be  capable  of  further 
division. 

8.  The  most  important  fact  which  we  gather  from 
these  data  is  that  the  cytoplasm  of  the  unfertilized  egg 
may  be  considered  as  the  embryo  in  the  rough  and  that 
the  nucleus  has  apparently  nothing  to  do  with  this 
predetermination.  This  must  raise  the  question  sug- 
gested already  in  the  third  chapter  whether  it  might 
not  be  possible  that  the  cytoplasm  of  the  eggs  is  the 
carrier  of  the  genus  or  even  species  heredity,  while  the 
^lendelian  heredity  which  is  determined  by  the  nucleus 


152  Organisms  from  Eggs 

adds  only  the  finer  details  to  the  rough  block.  Such  a 
possibility  exists,  and  if  it  should  turn  out  to  be  true 
we  should  come  to  the  conclusion  that  the  unity  of  the 
organism  is  not  due  to  a  putting  together  of  a  number 
of  independent  Mendelian  characters  according  to  a 
"pre-established  plan,"  but  to  the  fact  that  the  organ- 
ism in  the  rough  existed  already  in  the  cytoplasm  of 
the  egg  before  the  egg  was  fertilized.  The  influence 
of  the  hereditary  Mendelian  factors  or  genes  consisted 
only  in  impressing  the  numerous  details  upon  the  rough 
block  and  in  thus  determining  its  variety  and  individ- 
uality; and  this  could  be  accomplished  by  substances 
circulating  in  the  liquids  of  the  body  as  we  shall  see 
in  later  chapters. 


CHAPTER  VII 


REGENERATION 


I.  The  action  of  the  organism  as  a  whole  seems 
nowhere  more  pronounced  than  in  the  phenomena  of 
regeneration,  for  it  is  the  organism  as  a  whole  which 
represses  the  phenomena  of  regeneration  in  its  parts, 
and  it  is  the  isolation  of  the  part  from  the  influence 
of  the  whole  which  sets  in  action  the  process  of  regenera- 
tion. The  leaf  of  the  Bermuda  "life  plant" — Bryo- 
phyllum  calycinum — behaves  like  any  other  leaf  as  long 
as  it  is  part  of  a  healthy  whole  plant,  while  when  isolated 
it  gives  rise  to  new  plants.  The  power  of  so  doing  was 
possessed  by  the  leaf  while  a  part  of  the  whole,  and  it 
was  the  "whole"  which  suppressed  the  formative  forces 
in  the  leaf.  When  a  piece  is  cut  from  the  branch  of  a 
willow  it  forms  roots  near  the  lower  end  and  shoots  at 
the  upper  end,  so  that  a  tolerably  presentable  "whole" 
is  restored.  How  does  the  "whole"  prevent  the  basal 
end  of  the  shoot  from  forming  roots  as  long  as  it  is  part 
of  the  plant?     A  certain  fresh-water  flatworm  has  the 

mouth  and  pharynx  in  the  middle  of  the  body.     When  a 

153 


154  Regeneration 

piece  is  excised  between  the  head  and  the  pharynx  a 
new  head  is  formed  at  the  oral  end,  a  new  tail  at  the 
opposite  end,  and  in  the  middle  of  the  remaining  old 
tissue  a  new  mouth  and  pharynx  is  formed.  How  does 
the  "whole"  suppress  all  this  formative  power  in  the 
part  before  the  latter  is  isolated?  It  almost  seems  as 
if  the  isolation  itself  were  the  emancipation  of  the  part 
from  the  tyranny  of  the  whole.  The  explanation  of  this 
tyranny  or  of  the  correlation  of  the  parts  in  the  whole 
is  to  be  found,  however,  in  a  different  influence.  The 
earlier  botanists,  Bonnet,  Dutrochet,  and  especially 
Sachs,  ^  pointed  out  that  the  phenomena  of  correlation 
are  determined  by  the  flow  of  sap  in  the  body  of  a 
plant.  These  authors  formulated  the  idea  that  the 
formation  of  new  organs  in  the  plant  is  determined  by 
the  existence  of  specific  substances  which  are  carried 
by  the  ascending  or  descending  sap.  Specific  shoot- 
producing  substances  are  carried  to  the  apex,  while 
specific  root-producing  substances  are  carried  to  the 
base  of  a  plant.  When  a  piece  is  cut  from  a  branch  of 
willow  the  root-forming  substances  must  continue  to 
flow  to  the  basal  end  of  the  piece,  and  since  their  further 
progress  is  blocked  there  they  induce  the  formation  of 
roots  at  the  basal  end.     Goebel^  and  de  Vries  have 

» V'  Sachs,  J.,  "Stoff  und  Form  der  Pflanzenorgane,"  Gesammelte 
Abhandlungen,  1892,  ii.,  1160.  Arbeiten  a.  d.  bot.  Inst.  Wurzburg, 
1880-82. 

"  Goebel,  K.,  Einleilung  in  die  experimentelle  Morpliologie  der  Pflanzen, 
1908. 


Regeneration  i55 

accepted  this  view  and  the  writer  made  use  of  it  in  his 
first  experiments  on  regeneration  and  heteromorphosis 
in  anitnals. '  At  that  time  the  idea  of  the  existence  of 
such  specific  organ-forming  substances  was  received 
with  some  scepticism,  but  since  then  so  many  proofs 
for  their  existence  have  been  obtained  that  the  idea 
is  no  longer  questioned.  Such  substances  are  known 
now  under  the  name  of  "internal  secretions"  or  "hor- 
mones"; their  connection  with  the  theory  of  Sachs  was 
forgotten  with  the  introduction  of  the  new  nomenclature. 
It  may  be  well  to  enumerate  some  of  the  cases  in 
which  the  influence  of  specific  substances  circulating 
in  the  blood  upon  phenomena  of  growth  has  been 
proven.  One  of  the  most  striking  observations  in  this 
direction  is  the  one  made  by  Gudernatsch  on  the  growth 
of  the  legs  of  tadpoles  of  frogs  and  toads.  ^  The  young 
tadpoles  have  no  legs,  but  the  mesenchyme  cells  from 
which  the  legs  are  to  grow  out  later  are  present  at  an 
early  stage.  From  four  months  to  a  year  or  more  may 
elapse  before  the  legs  begin  to  grow.  Gudernatsch 
found  that  legs  can  be  induced  to  grow  in  tadpoles  at 
any  time,  even  in  very  young  specimens,  by  feeding 
them  with  the  thyroid  gland  (no  matter  from  what 

^  Loeb,  J.,  Untersuchungen  zur  physiologischen  Morphologie  der 
Tiere.  I.  Heteromorphose.  Wurzburg,  1891.  II.  Organbildung  und 
Wachsthum.  1892.  Reprinted  in  Studies  in  General  Physiology. 
Chicago,  1906. 

2  Gudernatsch,  J.  F.,  Zentralbl.  f.  Physiol.,  1912,  xxvi.,  323;  Arch.  f. 
Entwcklngsmech.,  1912,  xxxv.,  457;  Am.  Jour.  AnaL,  1914,  xv.,  431. 


156  Reo^eneration 


£> 


animal).  No  other  material  seems  to  have  such  an 
effect.  The  thyroid  contains  iodine,  and  Morse  ^  states 
that  if  instead  of  the  gland,  iodized  amino  acids  are 
fed  to  the  tadpole  the  same  result  can  be  produced. 
We  must,  therefore,  draw  the  conclusion  that  the  normal 
outgrowth  of  legs  in  a  tadpole  is  due  to  the  presence 
in  the  body  of  substances  similar  to  the  thyroid  in  their 
action  (it  may  possibly  be  thyroid  substance)  which 
are  either  formed  in  the  body  or  taken  up  in  the  food. 

Thus  we  see  that  the  mesenchyme  cells  giving  rise  to 
legs  may  lie  dormant  for  months  or  a  year  but  will  grow 
out  when  a  certain  type  of  substances,  e.  g.,  thyroid, 
circulates  in  the  blood.  There  may  exist  an  analogy 
between  the  activating  effect  of  the  thyroid  substance 
and  the  activating  effect  of  the  spermatozoon  or  butyric 
acid  (or  other  parthenogenetic  agencies)  upon  the  egg, 
but  we  cannot  state  that  the  thyroid  substance  activates 
the  mesenchyme  cells  by  altering  their  cortical  layer. 

The  fact  that  the  substance  of  the  thyroid  may 
induce  general  growth  in  the  human  is  too  well  known 
to  require  more  than  an  allusion  in  this  connection. 
When  growth  stops  in  children  as  a  consequence  of  a 
degeneration  of  the  thyroid,  feeding  of  the  patient  with 
thyroid  again  induces  growth.  It  may  also  suffice 
merely  to  call  attention  to  the  connection  between 
acromegaly  and  the  hypophysis. 

It  was  formerly  believed  that  the  nervous  systepi 

»  Morse,  M.,  Jour.  Biol.  Chem.,  1914,  xix.,  421. 


Regeneration  157 

acted  as  a  regulator  of  the  phenomena  of  metamor- 
phosis in  animals,  but  it  was  possible  to  show  by  simple 
experiments  that  the  central  nervous  system  does  not 
play  this  role  and  that  the  regulator  must  be  the  blood 
or  substances  contained  therein.  In  the  metamorphosis 
of  the  Amhly stoma  larva  the  gills  at  the  head  and  tail 
undergo  changes  simultaneously,  the  gills  being  ab- 
sorbed completely.  The  writer  showed  that  in  larvse 
in  which  the  spinal  cord  was  cut  in  two,  no  matter  at 
which  level, — the  sympathetic  nerves  were  in  all  prob- 
ability also  cut — the  two  organs  continued  to  undergo 
metamorphosis  simultaneously.  ^  Uhlenhuth  found  that 
if  the  eye  of  a  salamander  larva  is  transplanted  into 
another  larva  the  transplanted  eye  undergoes  its 
metamorphosis  into  the  typical  eye  of  the  adult  form, 
simultaneously  with  the  normal  eyes  of  the  individual 
into  which  it  was  transplanted.^  These  and  other 
observations  of  a  similar  character  leave  no  doubt  that 
substances  circulating  in  the  blood  and  not  the  central 
nervous  system  are  responsible  for  the  phenomena  of 
growth  and  metamorphosis. 

An  interesting  observation  on  the  r61e  of  internal 
secretion  in  growth  was  made  by  Leo  Loeb.^    When 

*  Loeb,  J.,  Arch.f.  Entwcklngsmech.,  1897,  iv.,  502. 

'  Uhlenhuth,  E.,  ibid.,  1913,  xxxvi.,  211. 

3  Loeb,  Leo,  Zentralhl.  f.  allg.  Path.  u.  path.  Anat.,  1907,  xviii.,  563; 
Zentralbl.  f.  Physiol.,  1908,  xxii.,  498;  1909,  xxiii.,  73;  1910,  xxiv.,  203; 
Arch.f.  Entwcklngsmech.,  1909,  xxvii.,  89,  463;  Jour.  Am.  Med.  Assoc, 
1908,  1.,  1897;  1909,  liii.,  1471. 


158  Regeneration 

the  fertilized  ovum  comes  in  contact  with  the  wall  of 
the  uterus  it  calls  forth  a  growth  there,  namely  the 
formation  of  the  maternal  placenta  (decidua).  This 
author  showed  that  the  corpus  luteum  of  the  ovary  gives 
off  a  substance  to  the  blood  which  alters  the  tissues  in 
the  uterus  in  such  a  way  that  contact  with  any  foreign 
body  induces  this  deciduoma  formation.  The  case  is  of 
interest  since  it  indicates  that  the  substance  given  off 
by  the  corpus  luteum  does  not  induce  growth  directly, 
but  that  it  allows  mechanical  contact  with  a  foreign  body 
to  do  so  while  without  the  intervention  of  the  corpus 
luteum  substance  no  such  effect  of  the  mechanical  stim- 
ulus would  be  observable.  The  action  of  the  substance 
of  the  corpus  luteum  is  independent  of  the  nervous 
system,  since  in  a  uterus  which  has  been  cut  out  and 
retransplanted  the  same  phenomenon  can  be  observed. 
Bouin  and  Ancel^  have  shown  that  the  corpus  luteum, 
which  in  the  case  of  pregnancy  continues  to  exist  for  a 
long  time,  is  responsible  for  the  changes  in  the  mammary 
gland  in  the  first  half  of  pregnancy,  when  an  active 
cell  proliferation  takes  place  in  the  gland.  This  process 
can  be  interrupted  by  destroying  the  corpus  luteum 
artificially.  During  the  second  half  of  gravidity  no 
further  cell  proliferation  takes  place,  but  the  cells  begin 
to  secrete  milk  while  during  the  period  of  cell  prolifera- 
tion such  secretions  do  not  occur. 

'  Quoted  from  M.  Caullery,  Les  Problemes  de  la  Sexualite,  Paris,  1913, 
p.  126. 


Regeneration  159 

Claude  Bernard  and  Vitzou  had  shown  that  the 
period  of  growth  and  moulting  of  the  higher  Crustacea 
is  accompanied  by  a  heaping  up  of  glycogen  in  the  liver 
and  subdermal  connective  tissue.  Smith  ^  found  that 
during  the  period  between  two  moultings,  when  there  is 
no  growth,  the  storage  cells  are  seen  to  be  filled  with 
large  and  numerous  fat  globules  instead  of  with  glyco- 
gen. He  also  found  that  in  the  Cladocera  "the  period 
of  active  growth  is  accompanied  by  glycogen — as 
opposed  to  fat — metabolism, "  He  observed,  moreover, 
that  if  Cladocera  are  crowded  at  a  low  temperature  the 
fat  metabolism  (with  inhibition  to  growth)  is  favoured, 
while  at  high  temperatures  and  with  no  crowding  of 
individuals  the  glycogen  metabolism  is  favoured.  In 
the  latter  case  a  purely  parthenogenetic  mode  of  propa- 
gation is  observed,  while  in  the  former  sexual  reproduc- 
tion takes  place.  The  effect  of  crowding  of  individuals 
is  possibly  due  to  products  of  excretion,  which  then  act 
on  gTowtYi  and  reproduction  indirectly  by  changing  the 
"glycogen  metabolism"  to  "fat  metabolism." 

All  these  cases  agree  in  this,  that  apparently  specific 
substances  induce  or  favour  growth,  not  in  the  whole 
body,  but  in  special  parts  of  the  body.  Sachs  suggested 
that  there  must  be  in  each  organism  as  many  specific 
organ-forming  substances  as  there  are  organs  in  the 
body. 

We  will  now  show  that  the  assumption  of  the  exist- 

^  Smith,  Geoffrey,  Proc.  Roy.  Soc,  B.  1915,  Ixxxviii.,  418. 


i6o  Regeneration 

ence  of  such  "organ-forming"  substances  (which  may 
or  may  not  be  specific)  and  of  their  flow  in  definite 
channels  explains  the  inhibitory  influence  of  the  whole 
on  the  parts  as  well  as  the  unbridled  regeneration  of  the 
isolated  parts. 

2.  We  have  seen  that  the  resting  egg  can  be  aroused 
to  development  and  growth  by  substances  contained  in 
a  spermatozoon  or  by  certain  other  substances  men- 
tioned in  the  preceding  chapter.  We  will  assume  that 
plants  contain  a  large  number  of  cells  or  buds  which  are 
comparable  to  the  resting  egg  cell,  but  which  can  be 
aroused  to  action  by  certain  substances  circulating  in 
the  sap;  and  that  the  same  is  effected  for  animal  cells 
by  substances  in  the  blood.  In  plants  the  cells  which 
can  be  aroused  to  new  growth  have  very  often  a  rather 
definite  location  while  in  lower  animals  they  are  more 
ubiquitous.  For  experimental  purposes  organisms 
where  these  buds  have  a  definite  location  are  more 
favourable,  since  we  are  better  able  to  study  the 
mechanism  underlying  the  process  of  activation  and 
inhibition  (correlation).  When  a  leaf  of  the  plant 
Bryophyllum  calycinum  is  cut  off  and  put  on  moist  sand 
or  into  water  or  even  into  air  saturated  with  water 
vapour,  new  plants  will  arise  from  notches  of  the  leaf. 
This  is  the  usual  way  of  propagating  the  plant  and  in  no 
other  part  of  the  leaf  except  the  notches  will  new  plants 
arise.  These  notches  therefore  contain  cells  comparable 
to  seeds  or  to  unfertilized  eggs  or  to  the  mesenchyme 


Regeneration 


i6i 


cells  which  give  rise  to  legs  in  the  tadpole  of  the  frog. 
The  question  arises:  Why  do  notches  in  the  leaf  never 
begin  to  grow  while  the  leaf  is  attached  to  an  intact 
plant,  and  why  do  they  grow  when  the  leaf  is  isolated? 
To  this  we  are  inclined  to  give  an  answer  in  the  sense 
of  Bonnet,  Sachs, 
deVries,  and 
Goebel,  namely 
that  the  flow  of 
(specific  ?)  s  u  b  - 
stances  in  the 
plant  determines 
when  and  where 
dormant  buds  or 
anlagen  shall  be- 
gin to  grow.  Such 
substances  may 
originate  or  may 
be  present  in  the  leaf ;  but  as  long  as  it  is  connected 
with  a  normal  plant  they  will  be  carried  by  the  cir- 
culation to  the  growing  points  of  the  stem  and  of  the 
roots  and  they  cannot  reach  the  notches ;  while  when  we 
detach  the  leaf,  either  a  new  distribution  or  a  new  flow 
of  liquids  will  be  established  whereby  the  substances 
reach  some  of  the  notches;  and  in  these  notches  new 
roots  and  a  new  shoot  will  be  formed.  When  we 
cut  o£E  a  leaf  and  put  it  into  moist  air,  not  all  but  only 
a  few  of  the  notches  will,  as  a  rule,  grow  out  (Fig.  i6) ; 


Fig.  1 6.     Growth  of  roots  and  shoots  In  a 

few  notches  of  an  isolated  leaf 

of  Bryophyllum  calycinum 


1 62 


Regeneration 


but  when  we  isolate  each  notch  leaving  as  much 
of  the  rest  of  the  leaf  as  possible  attached  to  it,  each 
notch  will  give  rise  to  a  new  plant.  ^  (Fig.  17.)  We 
see,  therefore,  that  it  does  not  even  require  a  whole 
plant  to  cause  inhibition  but  that  we  may  observe  the 
tyranny  of  the  whole  over  the  parts  in  a  single  leaf. 

The  explanation 
is  as  follows : 
When  we  isolate 
a  leaf,  some  of 
the  notches  will 
commence  t  o 
grow  into  new 
plants  and  this 
growth  will  ar- 
rest the  develop- 
ment  of  the 
other  notches  of 
the  leaf  in  the 
same  way  as 
their  development  was  suppressed  by  the  whole  plant. 
The  explanation  is  the  same;  those  notches  which 
begin  to  grow  first  will  attract  the  flow  of  substances 
to  themselves,  thus  preventing  the  other  notches  from 
getting  those  substances.  This  idea  is  supported  by 
the  fact  that  if  all  the  notches  are  isolated  from  the 
leaf    each   notch  will   give  rise   to  a  slowly  growing 

'  Loeb,  J.,  Bot.  Gazette,  1915,  Ix.,  249. 


Fig.  17.  If  all  the  notches  of  a  leaf  are  iso- 
lated from  each  other  each  notch  will  give  rise 
to  roots  and  a  shoot,  but  the  growth  will  be 
less  rapid  than  in  Fig.  16.  Figs.  16  and  17 
were  two  leaves  taken  from  the  same  node 
of  a  plant. 


Regeneration  163 

plant,  while  if  the  leaf  is  not  cut  into  pieces,  and  a  few 
notches  only  grow  out,  their  growth  is  much  more  rapid. 
In  all  these  experiments  the  idea  that  the  "isolation" 
in  itself  is  responsible  for  the  growth  still  presents  itself. 
It  can  be  disposed  of  by  the  following  experiment  which 
never  fails.  Three  leaves  of  Bryophyllum  calycmum 
are  suspended  in  an  atmosphere  saturated  with  water 
vapour  but  their  tips  are  submersed  in  water  (Figs. 
18,  19,  20).  The  first  leaf.  Fig.  20,  is  entirely  separated 
from  its  stem,  the  second  leaf,  Fig.  19,  remains  connected 
with  the  adjacent  piece  of  stem,  and  the  third  leaf, 
Fig.  18,  remains  also  connected  with  this  piece  of  stem 
but  the  latter  still  possesses  both  leaves.  The  first  leaf, 
Fig.  20,  produces  new  roots  and  shoots  in  the  submerged 
part  in  a  few  days;  the  second  leaf,  Fig.  19,  produces 
no  roots  or  shoots  for  a  long  time.  This  might  find  its 
explanation  by  the  assumption  that  the  first  leaf,  being 
more  isolated  than  the  second,  regenerates  more  quick- 
ly. But  this  explanation  becomes  untenable  owing  to 
the  fact  that  the  third  leaf,  Fig.  18,  being  less  isolated 
than  both  (possessing  a  second  leaf  in  addition  to 
the  stem),  forms  new  roots  and  shoots  also  more 
quickly  than  the  second  leaf.  The  phenomena  become 
intelligible  in  the  following  way.  The  fact  that  in  the 
second  leaf  shoots  and  roots  are  formed  very  late,  if  at 
all,  finds  its  explanation  not  in  the  lessened  isolation 
of  this  leaf,  but  in  the  fact  that  the  formation  of  a 
new  shoot  or  of  a  callus  in  the  piece  of  stem  takes  place 


164 


Regeneration 


more  quickly  than  the  formation  of  roots  and  shoots 
in  the  notches  of  a  completely  isolated  leaf.     The  stem 


Fig.  18 


Fig.  19 


Fig.  20 


acts  therefore  as  a  centre  of  suction  for  the  flow  of 
substances  from  the  leaf  and  this  prevents  or  retards 
the  formation  of  roots  and  shoots  in  the  notches.  In 
the  isolated  leaf  of  Bryophyllum  calycinum  no  callus 
formation  takes  place  and  hence  no  flow  of  the  sap 


Regeneration  165 

away  from  the  leaf  will  occur.  This  will  allow  one  or 
more  of  the  notch  buds  of  this  leaf  to  grow  out  and  then 
a  flow  will  be  established  towards  these  growing  buds. 

In  the  third  specimen,  Fig.  18,  the  presence  of  two 
leaves  suppresses  or,  as  a  rule,  retards  the  growth  of  a 
shoot  on  the  stem  and  possibly  also  the  flow  from  one 
leaf  may  block  to  some  extent  the  flow  from  the  op- 
posite leaf  if  the  piece  of  stem  is  very  short.  This  puts 
the  leaves  in  a  condition  not  as  good  as  that  in  leaf  Fig. 
20,  but  better  than  in  leaf  Fig.  19.' 

In  the  normal  plant  the  buds  in  the  notches  of  the 
leaf  remain  dormant  since  the  flow  of  the  "stimulating" 
substances  takes  place  towards  the  tips  of  the  stem  and 
root,  and  because  these  substances  are  retained  there  in 
excess.  This  is  probably  the  real  basis  of  the  mysterious 
dominance  of  the  "whole"  over  its  "parts"  or  of  the 
anlagen  of  the  tip  of  the  stem  over  those  farther  below. 
When  a  piece  of  the  stem  of  Bryopkyllum  is  cut  off  and 
its  leaves  are  removed,  the  two  apical  buds  will  grow 
out  first.  This  "dominance"  finds  its  explanation 
probably  in  the  anatomical  structure  and  the  mechan- 
ism of  sap  flow  which  tend  to  bring  the  "stimulating" 
substances  first  to  the  anlagen  in  the  tip.  In  Laminaria 
Setchell  has  been  able  to  show  directly  that  regenera- 
tion always  starts  from  that  tissue  which  conducts  the 
nutritive  material. 

When  we  cut  out  a  piece  of  a  stem  of  Bryopkyllum, 

*  With  larger  leaves  the  experiment  may  also  succeed  in  moist  air. 


1 66  Regeneration 

and  remove  all  the  leaves,  new  shoots  will  be  formed 
from  the  two  apical  buds  of  the  stem,  and  roots  will 
arise  from  the  most  basal  nodes ;  provided  that  the  stem 
is  suspended  in  air  saturated  with  water  vapour.  The 
growth  in  such  a  stem  deprived  of  all  leaves  is  slow.  If 
we  remove  all  the  leaves  on  such  a  piece  of  stem  except 
the  two  at  the  apical  end,  the  stem  will  form  only  roots, 
but  these  will  develop  much  more  rapidly  than  on  a 
stem  without  leaves.  If  we  remove  all  the  leaves 
except  the  two  at  the  basal  end,  the  stem  will  only 
form  shoots  (at  the  apical  end)  but  these  will  develop 
much  more  rapidly  than  in  a  leafless  stem.  Hence  the 
leaves  accelerate  the  growth  of  roots  towards  the  basal 
end  and  inhibit  it  towards  the  apical  end;  and  they 
favour  the  growth  of  shoots  towards  the  apical  end  and 
inhibit  it  in  the  nodes  located  nearer  the  base. 

We  thus  see  that  while  the  stem  inhibits  the  growth 
of  the  leaves  connected  with  it,  the  latter  accelerate  the 
growth  in  the  stem.  Both  facts  can  probably  be 
explained  on  the  same  basis ;  namely,  on  the  assumption 
that  it  is  the  flow  of  substances  from  the  leaf  to  the 
stem  which  inhibits  the  growth  of  the  notches  and  ac- 
celerates the  growth  of  the  buds  in  the  stem.  On  this 
assumption  it  would  also  follow  that  the  leaves  send 
root-forming  substances  towards  the  basal  and  shoot- 
forming  substances  towards  the  apex  of  the  stem.  It 
also  seems  to  follow  from  recent  as  yet  unpublished  ex- 
periments by  the  writer  that  the  root-forming  substances 


Regeneration 


167 


Fig.  21 


are  associated  or  identical  with  the  substances  which 
cause  geotropic  curvature  in  the  stem. 

These  observations  show  that 
the  phenomena  of  correlation  or 
of  the  influence  of  the  whole  over 
the  parts  is  due  to  peculiarities  of 
circulation  or  the  flow  of  sap;  and 
that  the  isolation  prevents  the  sap 
from  flowing  away  to  other  parts 
of  the  plant.  There  is  no  need  for 
assuming  the  existence  of  a  mys- 
terious force  which  directs  the  piece 
to  grow  into  a  whole. 

3.  Phenomena  of  inhibition  or  correlation  such  as 
we  have  described  in  Bryophyllum  are  not  lacking  in 
the  regeneration  of  animals,  as  experiments  on  Tubu- 
laria  show.  ^  Tuhularia  mesembryanthemum  (Fig.  21) 
is  a  hydroid  consisting  of  a  long  stem  terminating  at 

one  end  in  a  stolon 
which  attaches  it- 
self to  solid  bodies 
such  as  rocks,  a  t 
the  other  end  in  a  polyp.  The  writer  found  that  if 
we  cut  a  piece  from  a  stolon  and  suspend  it  in  an  aquar- 
ium it  forms  as  a  rule  a  polyp  at  either  end  (Fig.  22), 


Fig.  22 


^  Loeb,  J.,  Untersuchtingen  zur  physiologischen  Morphologic.  I. 
Heteromorphose.  1891.  II.  Organbildung  und  Wachsthum.  Wiirz- 
burg,  1892. 


i68  Regeneration 

but  the  velocity  with  which  the  two  polyps  are 
formed  is  not  the  same,  the  polyp  at  the  oral  end 
of  the  piece  being  formed  much  more  rapidly — a  day 
or  one  or  two  weeks  sooner — than  the  aboral  polyp. 
The  process  of  polyp  regeneration  at  the  aboral  pole 
could,  however,  be  accelerated  and  its  velocity  made 
equal  to  that  of  the  regeneration  of  the  oral  polyp  by 
suppressing  the  formation  of  the  latter.  This  was 
accomplished  by  depriving  the  oral  pole  of  the  oxygen 
necessary  for  regeneration,  e.  g.,  by  merely  putting  the 
oral  end  of  the  piece  of  stem  into  the  sand.  It  was, 
therefore,  obvious  that  the  formation  of  the  oral  polyp 
retarded  the  formation  of  the  aboral  polyp.  This 
inhibition  might  have  been  due  to  the  fact  that  a 
specific  organ-forming  material  needed  for  the  forma- 
tion of  a  polyp  existed  in  sufficient  quantity  in  the  stem 
for  the  formation  of  one  polyp  only  at  a  time.  This 
idea,  however,  was  found  to  be  incorrect  since  when  the 
stem  was  cut  into  two  or  more  pieces  each  piece  formed 
a  polyp  at  once  at  its  oral  pole  and  regenerated  the 
aboral  polyps  also,  but  again  with  the  usual  delay.  It 
seemed  more  probable  then  that  the  cause  of  the 
difference  in  the  rapidity  of  polyp  formation  at  both 
ends  lay  in  the  fact  that  certain  material  flowed  first 
to  the  oral  pole  and  induced  polyp  formation  here  but 
that  this  flow  was  reversed  as  soon  as  the  polyp  at  the 
oral  pole  was  formed  or  as  soon  as  the  formation  of  the 
oral  polyp  was  inhibited  by  lack  of  oxygen.    The  partial 


Regeneration 


169 


or  full  completion  of  the  formation  of  the  oral  polyp 
acted  as  an  inhibition  to  the  further  flow  of  material  to 
this  pole.  This  idea  was  supported  by  an  observation 
made  independently  by  Godlewski  and  the  writer  that 
if  a  piece  of  stem  be  cut  out  of  a  Tuhularia,  and  if  the 
piece  be  ligatured  somewhere  between  the 
two  ends,  the  oral  and  the  aboral  polyps 
are  formed  simultaneously.  This  would 
be  comprehensible  on  the  assumption  that 
the  retarding  effect  which  the  formation 
of  the  oral  has  on  the  aboral  polyp  was 
indeed  of  the  nature  of  a  flow  of  material 
towards  the  oral  pole. 

Miss  Bickford^  found  that  the  differ- 
ence in  time  between  the  formation  of 
the  two  polyps  disappears  also  when  the 
piece  cut  from  the  stem  becomes  so  small 
that  it  is  of  the  order  of  magnitude  of  a 
single  polyp.  In  that  case  two  incomplete  polyps  are 
formed  simultaneously  at  each  end  (Fig.  23).  The 
new  head  in  the  regeneration  of  Tuhularia  arises,  as 
Miss  Bickf ord  observed,  from  the  tissue  near  the  wound. 
At  some  distance  from  the  wound  in  the  old  tissue 
two  rows  of  tentacles  arise,  which  are  noticeable  as 
rows  of  longitudinal  lines  inside  the  stem  before  the 
head  is  formed.  Driesch  noticed  that  the  newly 
formed  head  is   the   smaller   the    smaller   the    whole 

'  Bickford,  E.  E.,  Jour.  MorphoL,  1894,  ix.,  417. 


Fig.  23 


I70  Regeneration 

piece.  (This  is  true,  however,  only  in  rather  small 
pieces.)  There  is,  therefore,  in  small  pieces  a  rough  pro- 
portionality between  size  of  head  and  size  of  regenerat- 
ing piece.  Driesch'  uses  this  interesting  fact  to  prove 
the  existence  of  an  entelechy,  while  we  are  inclined  to 
see  in  it  an  analogue  to  the  observation  of  Leo  Loeb, 
that  the  velocity  of  the  process  of  healing  in  the  case 
of  a  deficiency  of  the  epithelium  decreases  when  the 
size  of  the  uncovered  area  diminishes.  While  we  do 
not  wish  to  offer  any  suggestion  concerning  the  me- 
chanism of  these  quantitative  phenomena — they  may 
be  related  in  some  way  with  the  velocity  of  certain 
chemical  reactions — we  see  no  reason  for  assuming 
that  they  cannot  be  explained  on  a  purely  physico- 
chemical  basis. 

The  writer  noticed  that  certain  pigmented  cells 
from  the  entoderm  of  the  organism  always  gather  at 
that  end  where  a  new  polyp  is  about  to  be  formed. 
These  red  or  yellowish  cells  always  collect  first  at  the 
oral  end  of  a  piece  of  stem.  It  may  be  that  certain 
substances  given  off  by  the  pigmented  cells  at  the  cut 
end  are  responsible  for  the  polyp  formation,  but  this  is 
only  a  surmise. 

Another  suggestion  made  by  Child,  ^  is  that  there 
exists  an  axial  gradient  in  the  stem  whereby  the  cells 


'  Driesch,  H.,  Science  and  Philosophy  of  the  Organism,  i.,  127, 
'Child,  C.  M.,  "Die  physiologische  Isolation  von  Tcilen  des  Organ- 
ismus,"  Roux's  Vortrdge  und  Anfsdtze,  Leipzig,  191 1. 


Regeneration 


171 


regenerate  the  more  quickly  the  nearer  they  are  to  the 
oral  pole.  If  this  were  correct,  and  we  cut  a  long  piece 
from  the  stem  of  a  Tubularia  and  bisect  the  piece,  the 
oral  pole  of  the  anterior  half  should  regenerate  more 
quickly  than  the  oral  pole  of  the  posterior  half.  Accord- 
ing to  the  writer's  observations  on  a  Tubularian  {T. 
crocea)  growing  in  the  estuaries 
near  Oakland,  California,  both  oral 
ends  regenerate  equally  fast  in  such 
cases. 

4.  The  phenomena  of  regenera- 
tion in  Cerianthus  membranaceus, 
a  sea  anemone,  can  be  easily  under- 
stood from  the  experiments  on 
Tubularians,  if  we  imagine  the 
body  wall  of  Cerianthus  to  consist 
of  a  series  of  longitudinal  elements 
running  parallel  to  the  axis  of  sym- 
metry of  the  animal  from  the  tenta- 
cles to  the  foot.  The  number  of  these  elements  may 
be  supposed  to  correspond  to  the  number  of  tentacles 
in  the  outer  row  of  the  normal  animal.  Each  such  ele- 
ment behaves  like  a  Tubularian,  with  this  difference, 
however,  that  the  elements  in  Cerianthus  are  more 
strongly  polarized  than  in  Tubularia,  and  that  each 
one  is  able  to  form  a  tentacle  at  its  oral  pole  only. 
This  fact  can  be  nicely  illustrated  in  the  following  way : 
if  a  square  or  oblong  piece  (abed,  Fig.  24)  be  cut  from 


Fig.  24 


172 


Regeneration 


the  body  wall  of  a  Cerianthus  in  such  a  way  that 
one  side,  a  c,  of  the  oblong  is  parallel  to  the  longitudinal 
axis  of  the  animal,  tentacles  will  grow  on  one  of  the 
four  sides  only;  namely,  on  the  side  a  b.^  (Fig.  25.) 
The  other  three  free  edges  are  not  able  to  produce 
tentacles.     If  an  incision  be  made  in  the  body  wall  of 


a 


d 

Fig.  25  Fig.  26 

a  Cerianthus,  tentacles  will  grow  on  the  lower  edge  of 
the  incision  (Fig.  26). 

The  writer  tried  whether  or  not  by  tying  a  ligature 
around  the  middle  of  a  piece  of  an  Actinian  this  polarity 
could  be  suppressed;  but  the  experiments  did  not 
succeed,  inasmuch  as  the  cells  compressed  by  the  Hga- 
ture  died,  and  were  liquefied  through  bacterial  action  so 
that  the  pieces  in  front  and  behind  the  ligature  fell 
apart.  It  is  therefore  impossible  to  decide  whether  or 
not  a  current  or  a  flow  of  substances  in  a  certain  direc- 


'  Loeb,  J.,  "Untersuchungen  zur  physiologlschen   Morphologie  der 
Tiere." 


Regeneration 


173 


tion  through  these  elements  is  responsible  for  this 
polarity,  though  this  may  be  possible.  The  writer 
found,  however,  that  one  condition  is  necessary  for  the 
growth  and  regeneration  of  tentacles  which  also  plays  a 
role  in  the  corresponding  phenomena  in  plants,  namely 
turgidity.  The  tentacles  of  Cerianthus  are  hollow 
cylinders  closed  at  the  tip,  and  by 
liquid  being  pressed  into  them  they 
can  be  stretched  and  appear  turgid.  If, 
however,  an  incision  is  made  in  the 
body,  the  tentacles  above  the  incision 
can  no  longer  be  stretched  out.  In  one 
experiment  the  oral  disk  of  a  Cerian- 
thus was  cut  off;  very  soon  new  tenta- 
cles began  to  grow  at  the  top,  and  after 
having  reached  a  certain  size,  an  incision 
was  made  in  the  animal.  The  tentacles 
above  the  incision  collapsed  in  conse- 
quence and  ceased  to  grow,  while  growth 
of  the  others  continued.  On  the  lower 
edge  of  the  incision  new  tentacles  began  to  grow. 

It  seems  also  possible  that  Morgan's  well-known  ex- 
periment on  regeneration  mPlanaria  can  be  explained  by 
a  flow  of  substances.  He^  found  that  if  a  piece  a  c  d  h 
be  cut  out  of  a  fresh-water  Planarian  at  right  angles 
to  the  longitudinal  axis  (Fig.  27),  at  the  front  end  a  new 
normal  head,  at  the  back  end  a  new  tail,  will  be  regen- 

^  Morgan,  T.  H.,  Regeneration,  New  York,  1901. 


Fig.  27 


174 


Regeneration 


Fig.  28 


erated  (Fig,  28) ;  but  that  if  a  piece  acd  bhe  cut  from  a 
Planarian  obliquely  (Fig.  29)  instead  of  at  right  angles  to 
the  longitudinal  axis  a  tiny  head  is 
formed  at  the  foremost  comer  of  the 
piece  a  and  a  tiny  tail  at  the  hindmost 
comer  b  (Fig.  30) .  Why  is  it  that  in  the 
oblique  piece  the  head  is  formed  in  the 
corner  and  not  all  along  the 
cut  surface  as  is  the  case  when 
the  cut  is  made  at  right  angles 
to  the  longitudinal  axis?  The 
writer  is  inclined  to  believe  that 
the  right  answer  to  this  ques- 
tion has  been  given  by  Bar- 
deen.  ^  This  author  has  pointed 
out  the  apparent  role  that  the 
circulatory  (or  so-called  di- 
gestive) canals  in  Planarians 
play  in  the  localization  of  the 
phenomena  of  regeneration,  in- 
as-much 

as  the  new  head  always  forms 
symmetrically  at  the  opening  of 
the  circulatory  vessel  or  branch 
which  is  situated  as  much  as 
Fig.  30  possible  at  the  foremost  end  of  the 

'Bardeen,  C.  R.,Am.  Jour.  Physiol.,  igoi.v.,  i;  Arch.  f.  EntwcklngS' 
mech.,  1903,  xvi.,  i. 


Fig.  29 


Regeneration  175 

regenerating  piece  of  worm.  He  assumes  that  through 
muscular  action  the  liquids  of  the  body  are  forced  to 
stream  toward  this  end,  and  that  this  fact  has  some  con- 
nection with  the  formation  of  a  new  head.  There  can 
be  no  doubt  that  the  facts  here  mentioned  agree  with 
Bardeen's  suggestion.  The  oblique  pieces  in  Morgan's 
experiments  which  at  first  have  the  heads  and  tails 


Fig.  31      /  Fig.  32 


outside  the  line  of  symmetry  of  the  middle  piece, 
gradually  assume  a  normal  position  (Figs.  31,  32). 
The  writer  is  inclined  to  believe  that  this  is  due  to 
mechanical  conditions.  The  head  a  e  c  oi  such  an 
oblique  piece  is  asymmetrical,  the  one  side  a  e  being  less 
stretched  than  the  other  e  c.  The  higher  tension  of  the 
piece  e  c  will  have  the  effect  of  bringing  e  nearer  c,  since 
we  know  that  acid  formation  and  hence  energy  pro- 
duction increases  in  proportion  to  surface,  i.  e.,  it  must 
be  the  greater  the  more  it  is  stretched.  The  reverse  is 
true  for  the  tail  d  f  b,  and  the  effect  here  will  be  that/ 


176  Regeneration 

will  be  pulled  nearer  d.  In  this  way  purely  mechanical 
conditions  are  responsible  for  the  fact  that  the  soft 
tissues  of  the  animal  are  gradually  restored  to  their 
true  orientation. 

As  a  final  possible  example  of  the  influence  of  internal 
secretion  or  substances  contained  in  the  blood  may 
be  mentioned  the  following  curious  observation  of 
Przibram. '  In  a  crustacean,  Alpheus,  the  two  chelae 
(pincers)  are  not  equal  in  size  and  form,  one  being 
very  much  larger  than  the  other.  Przibram  found  that 
when  he  cut  off  the  larger  pincer  in  such  crustacean? 
the  remaining  pincer  assumes  in  the  next  moulting 
the  size  and  shape  of  the  removed  large  pincer;  while 
in  place  of  the  removed  pincer  one  of  the  small  type 
is  produced.  Hence  a  reversal  of  the  two  pincers  is 
thus  brought  about.  If  later  on  the  large  pincer  is 
again  cut  off  the  process  is  repeated  and  the  original 
dissymmetry  is  restored.  Przibram  was  able  to  show 
that  the  nervous  system  has  no  connection  with  this 
phenomenon. 

The  elements  which  have  entered  into  the  discussion 
thus  far  are,  first,  the  flow  of  substances  in  preformed 
channels;  second,  the  existence  of  general  or  specific 
substances  required  for  the  growing  or  regenerating 
organ.  A  third  element  is  to  be  added;  namely  the 
"suction"  effect  upon  these  substances  of  a  developing 
organ.    Thus  we  see  that  if  one  or  a  few  of  the  notches 

'Przibram,  H.,  Arch.  J.  Entwcklngsmech.,  1901,  xi.,  329. 


Regeneration  177 

in  a  leaf  of  Bryophyllum  grow  out  the  other  notches  of 
the  leaf  are  inhibited  from  growing.  There  is  enough 
material  present  in  the  leaf  for  all  the  notches  to  grow 
into  shoots  as  is  proved  by  the  fact  that  all  will  grow 
out  if  they  are  isolated  from  each  other.  This  was 
explained  on  the  assumption  that  the  notches  of  a 
whole  which  happen  to  develop  first,  create  a  flow  of 
these  substances  from  the  rest  of  the  leaf  to  themselves 
and  thus  prevent  any  getting  to  the  other  notches.  We 
stated  that  this  is  supported  by  the  fact  that  the  few 
notches  growing  out  in  an  undivided  leaf  grow  more 
rapidly  than  the  many  shoots  growing  from  each  notch 
of  a  divided  leaf.  But  why  should  a  growing  shoot  or  a 
growing  point  in  general  produce  such  a  suction?  I 
think  this  may  be  possible  on  the  assumption  that  the 
consumption  of  these  substances  by  the  growing  organs 
causes  a  low  osmotic  pressure  of  these  substances  in  the 
growing  region  and  this  fall  of  osmotic  potential  will 
act  as  a  cause  for  the  further  flow.  This  brings  about 
the  apparent  "suction"  effect  of  the  growing  elements 
upon  the  flow  of  substances. 

5.  We  mentioned  that  when  a  piece  is  cut  from  a 
Planaria  between  pharynx  and  head  a  new  mouth  is 
formed  in  the  middle.  It  should  also  be  mentioned  that 
according  to  Child  the  piece  after  regeneration  is 
smaller  than  it  was  before.*  This  indicates  that 
material  in  the  old  cells  has  been  digested  or  has  under- 

*  Child,  C.  M.,  Senescence  and  Rejuvenescence.     Chicago,  1915. 


178 


Regeneration 


gone  hydrolysis  in  order  to  furnish  the  nutritive  material 
for  the  new  head  and  tail,  since  the  piece  cannot  take 
up  any  food  from  the  outside  before  a  mouth  is  formed. 
These  phenomena  of  autodigestion — the  process  itself 
will  be  discussed  in  the  last  chapter — seem  to  occur  in 
many  (if  not  all)  phenomena  of  regeneration.    It  may 

be  that  the  collect- 
ing  of   red  cells  at 
the  end  in  a  Tubu- 
larian  where  regen- 
eration is  about   to 
begin  has  to  do  with 
the    furnishing    o  f 
material     by     self- 
digestion,  since  these 
cells  are   partly   at 
least    destroyed   i  n 
the   process.      It  is  of  interest  to  look  for  more  ex- 
amples   of    autodigestion    accompanying   phenomena 
of  regeneration. 

The  writer  has  observed  more  closely  the  transforma- 
tion of  an  organ  into  more  undifferentiated  material  in 
Campanularia  (Fig.  33),  a  hydroid.'  This  organism 
shows  a  remarkable  stereotropism.  Its  stolons  attach 
themselves  to  solid  bodies,  and  the  stems  appear  on 
the  side  of  the  stolon  exactly  opposite  the  point  or 
area    of   contact   with   the    solid   body.      The   stems 

'  Loeb,  J.,  Am.  Jour.  Physiol.,  1900,  iv.,  60. 


Fig.  33 


Regeneration 


179 


grow,  moreover,  exactly  at  right  angles  to  the  solid 
surface  element  to  which  the  stolon  is  attached.  If  such 
a  stem  be  cut  and  put  into  a  watch  glass  with 
sea  water,  it  can  be  observed  that  those  polyps 

which   do  not  fall 
off  go   through   a 
series    of    changes 
which  make  it  ap- 
pear as  if  the  dif- 
ferentiated material  of  the  polyp  were 
transformed  into  undifferentiated  ma- 
terial.    The  tentacles  are  first  put  to- 
gether like  the  hairs  of  a  camel 's-hair 
Fig.  34  brush  (Fig.  34) ,  and  gradually  the  whole 

fuses  to  a  more  or  less  shapeless  mass 
which  flows  back  into  the  periderm  (Fig.  35).  It 
follows  from  this  that  in  this  process  certain  solid 
constituents  of  the 
polyp,  e.  g.,  the  cell 
walls,  must  be 
liquefied.  This  un- 
differentiated mate- 
rial formed  from  the 
polyp  may  afterward 

fiow  out  again,  giving  rise  to  a  stolon  or  a  polyp ;  to  the 
former  where  it  comes  in  contact  with  a  solid  body,  to 
the  latter  where  it  is  surrounded  by  sea  water.  These 
observations  suggest  the  idea  of   reversibiHty   of   the 


Fig.  35 


i8o  Regeneration 

process  of  differentiation  of  organs  and  tissues,  in  cer- 
tain forms  at  least.  We  have  to  imagine  that  some 
of  the  cells  or  interstitial  tissue  is  digested  and  that  as 
a  consequence  the  organ  loses  its  characteristic  shape. 

Giard  and  Caullery  have  found  that  a  regressive 
metamorphosis  occurs  in  Synascidians,  and  that  the 
animals  hibernate  in  this  condition.  The  muscles  of 
the  gills  of  these  animals  are  decomposed  into  their 
individual  cells.  The  result  is  the  formation  of  a 
parenchyma  which  consists  of  single  cells  and  of 
cell  aggregates  resembling  a  morula.  * 

Driesch,  ^  experimenting  on  the  regeneration  of  an 
Ascidian,  found  that  when  he  cut  off  the  gills  and 
siphons  of  the  animal  the  portion  removed  was  able 
to  regenerate  a  whole  animal.  The  gill-piece  excised 
contained  no  heart,  no  intestine,  and  no  stolon,  and  all 
these  organs  were  regenerated  from  the  gills.  In  a 
number  of  cases  the  regeneration  took  place  by  bud 
formation  at  the  edge  of  the  wound,  but  in  other  cases 
the  gills  were  transformed  into  an  undifferentiated  mass 
of  tissue  from  which  the  missing  parts  of  the  animals 
arose  by  budding  and  new  gills  were  formed. 

It  is  probable  that  the  two  cases  are  only  quantita- 
tively different.  In  both,  autodigestion  of  certain  cell 
constituents  and  possibly  of  whole  cells  must  take 
place  in  order  to  obtain  material  for  the  formation  of  the 

'  The  writer  quotes  this  after  Driesch. 

*  Driesch,  H.,  Arch.  J.  Entwcklngsmech.,  1902,  xiv.,  247, 


Regeneration  i8i 

lost  part  of  the  Ascidian.  If  an  interstitial  tissue  is 
digested  it  becomes  a  question  of  how  much  of  this  tissue 
undergoes  hydrolysis.  If  there  is  Httle  destroyed  the 
old  shape  of  the  gills  remains,  if  too  much  is  digested 
the  old  gills  become  a  shapeless  mass  in  which  a  certain 
number  of  the  old  cells  are  maintained  and  give  rise  to 
the  new  animal  by  cell  division.  The  material  for  the 
new  organs  must  of  course  be  furnished  from  old  cells 
which  have  been  digested. 

If  regeneration  takes  place  in  pieces  which  take  up 
no  food  the  newly  formed  organs  must  originate  from 
material  absorbed  from  cells  of  the  animal  which  are 
hydrolyzed  and  whose  material  serves  as  food  for  those 
cells  which  grow.  Very  often  this  process  of  digestion 
takes  place  without  loss  of  the  total  form  of  the  organ 
and  is  overlooked  by  the  pure  morphologists.  In 
Campanularia  also  the  process  of  collapse  described 
above  is  only  apparent  in  a  fraction  of  the  cases  as  in 
Driesch's  observations  on  Clavellina.  ^  It  is  also  possible 
that  the  red  and  yellow  entoderm  cells  which  gather  at 
the  end  where  the  new  polyp  forms  furnish  the  material 
which  is  utilized  for  the  process  of  growth  of  the  cells 
from  which  the  tentacles  arise  (with  or  without  giving 
off  specific  "hormones"  besides). 


'  One  author,  Miss  Thatcher,  in  trying  to  repeat  these  observations, 
did  not  notice  the  total  collapse  of  the  tissues  and  concluded  that  my 
observations  must  have  been  wrong.  The  writer  is  fairly  certain  that 
his  observations  were  correct. 


1 82  Regeneration 

6.  We  have  mentioned  the  ideas  concerning  a 
design,  or  "entelechy, "  acting  as  a  guide  to  the 
developing  egg  and  have  shown  that  this  revival  of 
Platonic  and  Aristotelian  philosophy  in  biology  was 
due  to  a  misconception;  namely,  that  the  egg  consisted 
of  homogeneous  material  which  was  to  be  differentiated 
into  an  organism.  For  this  supernatural  task  super- 
natural agencies  seemed  required.  But  we  have  seen 
that  the  unfertilized  egg  is  already  differentiated  in  a 
way  which  makes  the  further  differentiation  a  natural 
affair.  This  idea  of  a  quasi  superhuman  intelligence 
presiding  over  the  forces  of  the  living  is  met  with  in  the 
field  of  regeneration,  and  here  again  it  is  based  upon  a 
misconception.  The  lens  of  the  eye  is  formed  in  the 
embryo  from  the  epithelium  lying  above  the  so-called 
optic  cup  (the  primitive  retina).  Where  this  retina 
touches  the  epithelium  the  latter  begins  to  grow  into 
the  cup,  the  ingrowing  piece  of  epithelium  is  cut  off  and 
forms  the  lens,  which  probably  under  the  influence  of 
substances  secreted  by  the  optic  cup  becomes  trans- 
parent. Certain  animals  like  the  salamander  are  able 
to  form  a  new  lens  when  the  old  one  has  been  removed 
by  operation,  but  the  new  lens  is  formed  in  an  entirely 
different  way;  namely,  from  the  upper  edge  of  the  ins. 
G.  Wolf,  who  observed  this  regeneration  used  it  to 
endow  the  organism  with  a  knowledge  of  its  needs;  the 
idea  of  a  Platonic  preconceived  plan  or  an  Aristotelian 
purpose  suggested  itself.    But  it  can  be  shown  that  the 


Regeneration  1S3 

organism  does  in  this  case  what  it  is  compelled  to  do 
by  its  physical  and  chemical  structure. 

Uhlenhuth^  has  shown  by  way  of  tissue  culture  that 
the  cells  of  the  iris  cannot  grow  and  divide  as  long  as 
they  are  full  of  pigment  granules  as  they  normally  are. 
When  the  fine  superficial  membrane  of  the  iris  is  torn 
the  pigment  granules  fall  out  and  the  cells  can  now  grow 
and  multiply.  If  the  lens  is  taken  out  of  the  eye  of  the 
salamander  the  fine  membrane  of  the  iris  is  torn  and 
the  pigment  cells  at  the  edge  (especially  the  upper  edge) 
lose  their  pigment  granules  which  fall  down  on  account 
of  their  specific  gravity.  As  soon  as  this  happens  the 
cells  will  proliferate.  A  spherical  mass  of  cells  is  formed 
which  become  transparent  and  which  will  cease  to  grow 
as  soon  as  they  reach  a  certain  size.  The  unanswered 
question  is:  Why  does  the  mass  of  cells  become  trans- 
parent so  that  it  can  serve  as  a  lens?  The  answer  is  that 
young  cells  when  put  into  the  optic  cup  always  become 
transparent  no  matter  what  their  origin;  it  looks  as  if 
this  were  due  to  a  chemical  influence  exercised  by  the 
optic  cup  or  by  the  liquid  it  contains.  Lewis  has  shown 
that  when  the  optic  cup  is  transplanted  into  any  other 
place  under  the  epithelium  of  a  larva  of  a  frog  the 
epithelium  will  always  grow  into  the  cup  where  the 
latter  comes  in  contact  with  the  epitheHimi;  and  that 
the  ingrowing  part  will  always  become  transparent. 
This  leaves  us  then  with  one  puzzle  still:  Why  is  the 

^  Not  yet  published. 


t84  Regeneration 

growth  of  the  lens  Hmited?  The  limitation  in  the 
growth  of  organs  is  one  of  the  most  important  problems 
in  growth  and  organ  formation,  though  unfortunately 
our  knowledge  of  this  topic  is  inadequate. 

7.  The  botanist  J.  Sachs  was  the  first  to  definitely 
state  that  in  each  species  the  ultimate  size  of  a  cell  is  a 
constant,  and  that  two  individuals  of  the  same  species 
but  of  different  size  differ  in  regard  to  the  number,  but 
not  in  regard  to  the  size  of  their  cells.  ^  Amelung,  a 
pupil  of  Sachs,  determined  the  correctness  of  Sachs's 
theory  by  actual  counts.  Sachs,  in  addition,  recognized 
that  wherever  there  were  large  masses  of  protoplasm, 
e.  g.,  in  siphoneae  and  other  coeloblasts,  many  nuclei 
were  scattered  throughout  the  protoplasm.  He  inferred 
from  this  that  "each  nucleus  is  only  able  to  gather 
around  itself  and  control  a  limited  mass  of  protoplasm."* 
He  points  out  that  in  the  case  of  the  animal  egg  the 
reserve  material — fat  granules,  proteins,  and  carbo- 
hydrates— are  partly  transformed  into  the  chromatin 
substances  of  the  nuclei,  and  that  the  cell  division  of  the 
egg  results  in  the  cells  reaching  a  final  size  in  which  each 
nucleus  has  gathered  around  itself  that  mass  of  proto- 
plasm which  it  is  able  to  control.  Morgan^  and 
Driesch''  tested  and  confirmed  the  idea  of  Sachs  for 

*  V.  Sachs,  J.,  "  Physiologische  Notizen,"  vi.,  Flora,  1893. 
'Ibid.,  ix.,  425,  Flora,  1895. 

3  Morgan,  T.  H.,  Arch.f.  Entwcklngsmech.,  1895,  ii.,  81 ;  1901,  xiii.,  416; 
1903,  xvi.,  117. 

<Driesch,  H.,  Arch.  f.  Entwcklngsmech.,  1898,  vi.,  198;  1900,  x.,  361. 


Regeneration  185 

the  eggs  of  Echinoderms.  We  stated  in  the  previous 
chapter  that  Driesch  produced  artificially  larvae  of  sea 
urchins  of  one-eighth,  one-fourth,  and  one-half  their 
normal  size  by  isolating  a  single  cleavage  cell  in  one  of 
the  first  stages  of  segmentation  of  the  fertilized  sea- 
urchin  egg.  He  coimted  in  each  of  the  dwarf  gastmlae 
resulting  from  these  partial  eggs  the  number  of  mesen- 
chyme cells  and  found  that  the  larvae  from  a  one-half 
blastomere  possessed  only  one-half,  those  from  a  one- 
fourth  blastomere  only  one-fourth,  and  those  from  a 
one-eighth  blastomere  only  one-eighth  of  the  number  of 
cells  which  a  normal  larva  developing  from  a  whole  egg 
possessed.  Moreover,  he  could  show  that  when  two 
eggs  were  caused  to  fuse  so  as  to  produce  a  single  larva 
of  double  size,  the  gastrulse  of  such  larvae  had  twice  the 
number  of  mesenchyme  cells.  Driesch  drew  the  con- 
clusion from  his  observations  that  each  morphogenetic 
process  in  an  egg  reaches  its  natural  end  when  the 
cells  formed  in  the  process  have  reached  their  final 
size. 

Since  each  daughter  nucleus  of  a  dividing  blastomere 
has  the  same  number  of  chromosomes  as  the  original 
nucleus  of  the  egg,  it  is  clear  that  in  a  normally  fertilized 
egg  each  nucleus  has  twice  the  mass  of  chromosomes 
that  is  contained  in  the  nucleus  of  a  merogonic  egg,  i.  e., 
an  enucleated  fragment  of  protoplasm  into  which  a 
spermatozoon  has  entered  and  which  is  able  to  develop. 
Such  a  fragment  has  only  the  sperm  nucleus.     This 


1 86  Regeneration 

phenomenon  of  merogony  was  discovered  by  Boveri 
and  was  elaborated  by  Delage.^  Boveri,  in  comparing 
the  final  size  of  the  cells  in  normal  and  merogonic  eggs 
after  the  cell  divisions  had  come  to  a  standstill,  found 
that  this  size  is  always  in  proportion  to  the  original 
mass  of  the  chromatin  contained  in  the  egg ;  the  cells  of 
the  merogonic  embryo,  e.  g.,  the  mesenchyme  cells,  are 
only  half  the  size  of  the  same  cells  in  the  normally 
fertilized  embryo.  Driesch  furnished  a  further  proof 
of  Boveri's  law,  that  the  final  ratio  of  the  mass  of  the 
chromatin  substance  in  a  nucleus  to  the  mass  of  proto- 
plasm is  a  constant  in  a  given  species.  Driesch  com- 
pared the  size  of  the  mesenchyme  cells  in  a  sea-urchin 
embryo  produced  by  artificial  parthenogenesis  with 
those  of  a  normally  fertilized  egg  and  found  them  half 
of  the  size  of  the  latter.  When  the  fertilized  eggs  and 
the  parthenogenetic  eggs  are  equal  in  size  from  the 
start, — which  is  practically  the  case  if  eggs  of  the  same 
female  are  used, — the  process  of  the  formation  of 
mesenchyme  cells  comes  to  a  standstill  when  their 
number  in  the  normally  fertilized  eggs  is  half  as  large 
as  the  final  number  in  the  parthenogenetic  egg.'^ 
Boveri's  results  as  well  as  those  of  Driesch  were  ob- 
tained by  counting  the  cells  formed  by  eggs  of  equal 
size  and  not  by  simply  measuring  the  size  of  the  cells. 
It  is  most  remarkable  that  certain  apparent  exceptions 

*  Delage,  Y.,  Arch.  Zool.  exper.,  1899,  vii.,  383. 

*  Driesch,  H.,  Arch.  J.  Entwcklngsmech.,  1905,  xix.,  648. 


Regeneration  187 

to  B oven's  law  which  Driesch  has  actually  found  had 
been  predicted  by  Boveri. 

These  facts  show  that  the  growth  of  an  organ  comes 
to  a  standstill  when  a  certain  size  is  reached  or  a  certain 
number  of  cells  are  formed.  We  cannot  yet  state  why 
this  should  be,  but  we  are  able  to  add  that  the  formation 
of  a  lens  of  normal  size  in  the  regeneration  of  the  eye 
is  in  harmony  with  the  phenomena  in  the  embryo. 
There  seems  therefore  no  reason  for  stating  that  the 
regeneration  of  the  lens  cannot  be  explained  on  a  purely 
physicochemical  basis.  The  only  justification  for  such 
a  statement  on  the  part  of  Wolf  is  that  he  was  not  in 
possession  of  the  more  complete  set  of  facts  now  avail- 
able through  the  work  of  Fischel  and  Uhlenhuth. 

The  healing  of  a  wound  is  a  process  essentially  simi- 
lar to  the  regeneration  of  the  lens.  Normally  the  cells 
which  begin  to  proliferate  after  a  wound  is  made  in  the 
skin  lie  dormant,  inasmuch  as  they  neither  grow  nor 
divide.  When  a  wound  is  made  certain  layers  of 
epidermal  cells  undergo  rapid  cell  division.  Leo  Loeb^ 
has  studied  this  case  extensively.  He  found  that  if  the 
skin  is  removed  anywhere,  epidermis  cells  from  the 
wound  edge  creep  upon  the  denuded  spot  and  form  a 
covering.  This  may  be  a  tropism  (stereotropism)  or  it 
may  be  a  mere  surface  tension  phenomenon.  Next  a 
rapid  process  of  cell  division  begins  in  the  cells  adjacent 
to  the  wound  these  cells  having  been  heretofore  dormant. 

^  Loeb,  Leo,  Arch.  f.  EntwchlngsmecTi.,  1898,  vi.,  297. 


1 88  Regeneration 

He  is  inclined  to  attribute  this  increase  in  the  rate  of 
cell  division  to  the  stretching  of  the  epithelial  cells,  and 
he  is  supported  in  this  reasoning  by  the  observation  that 
the  larger  the  wound  the  more  rapid  the  process  of 
healing.*  During  wound  healing  the  mitoses  first 
increase  markedly  in  the  old  epithelium.  With  the 
closure  of  the  wound  a  sudden  fall  in  the  mitoses  takes 
place.  The  closure  of  the  woxind  causes  an  increase  in 
the  number  of  epithelial  rows  over  the  defect.  This 
increase  is  therefore  reached  at  an  earlier  period  in  the 
larger  wound  since  the  process  of  mitosis  is  more  rapid 
here.  Leo  Loeb  thinks  that  the  pressure  of  the  epithelial 
cells  upon  each  other  leads  to  a  rapid  diminution  in  the 
mitotic  proliferation.' 


»  ^jain,  K-  C,  anr!  Loeb,  Leo,  Jour.  Ezper.  Med.,  1916,  xxiii.,  107; 
Loeb,  L^  and  Addison,  W,  H.  P.,  Arch.f.  Entacklngsmech.,  191 1,  xzxiL, 
44;  1913,  xiiviL,  635. 

» Tbe  excessive  f onnation  of  epithelial  cells  in  the  healing  of  woonds 
has  led  the  older  pathologists  to  the  geoaaHzatim  that  if  scmaething  is 
removed  in  the  body  an  excessive  compensation  will  take  place.  The 
f  onnatioo.  of  antToodies  has  even  been  explained  on  this  basis  by  Weiggert 
and  Ehrlich  in  their  side-chain  theory.  As  a  matter  of  fact,  this  generali- 
aatioa  is  entirely  tncorrect  and  in  regeneration  of  starfish,  actinians, 
flatncnos,  amirfTAt,  and  possibly  in  all  forms  the  reverse  is  true;  e.  g., 
if  we  art  off  the  anterior  half  of  the  body  in  Cerianthus  less  is  reproduced 
than  was  cot  away  namely  only  tentacles  and  the  mouth,  but  not  the 
imKsarvg  piece  of  the  body.  Weiggert's  concepticn  cl  regeneration  was 
pcobaUy  based  on  the  i^ienomeaon  d  the  healing  c^  wounds,  but  tbe 
excessive  epithelium  formatioa  in  this  case  is  not  the  expressiixi  d  a 
general  law  d  r^eneiatkxi  but  of  the  peculiar  mechanical  conditions 
wfaidi  lead  to  mitoses.  It  would  be  a  very  strange  coincidence  indeed  if 
a  theory  of  antToodj  formatioa  based  on  such  an  erroneous  generaliza- 
tiao  sfaoold  be  correct 


Regeneration  189 

Should  it  be  possible  that  this  is  more  generally  the 
case,  e.  g-,  also  in  the  lens  after  it  has  reached  a  certain 
size?  The  conditions  limiting  growth  require  further 
investigation. 

It  is  hardly  necessary  to  point  out  that  in  these  cases 
we  are  seemingly  dealing  with  cases  of  the  inhibition  of 
growth  which  cannot  be  explained  by  the  tyranny  of 
the  whole  over  the  parts,  and  that  there  must  be  condi- 
tions at  work  other  than  the  mere  flow  of  substances 
which  can  cause  a  cessation  of  growth.  This  can  be 
illustrated  by  certain  observations  on  the  egg. 

8.  The  history  of  the  egg  shows  a  reversible  condi- 
tion of  rest  and  of  activity.  The  primordial  egg  cell 
multiplies  actively  imtil  a  large  number  of  eggs  are 
formed  in  the  ovary  which  may  reach  into  the  millions 
in  the  case  of  sea  urchins  or  certain  annelids.  These 
cell  divisions  then  stop  and  the  egg  goes  into  the  resting 
stage  in  which  it  deposits  the  reserve  material  for  the 
development  of  the  embryo.  From  this  condition  it 
can  only  be  called  into  activity  again  by  the  spermato- 
zoon or  the  agencies  of  artificial  parthenogenesis. 

It  seemed  of  intei'est  to  find  out  whether  or  not  the 
development  of  the  egg  may  be  reversed  once  more 
after  it  has  been  activated.  From  all  that  has  been  said 
in  the  chapter  on  artificial  parthenogenesis,  such  a 
reversal  should  take  place  in  the  cortical  layer.  The 
result  of  these  experiments  seems  to  be  that  if  a  complete 
destruction  or  change  in  the  cortical  layer  has  once 


190  Regeneration 

taken  place  — such  as  that  caused  by  the  entrance  of 
a  spermatozoon  into  the  egg — no  reversal  is  possible; 
although  the  development  of  the  fertilized  egg  may  be 
suppressed  for  a  long  time  by  either  low  temperature 
or  lack  of  oxygen,  or,  in  the  case  of  seeds  and  spores,  by 
lack  of  water.  But  as  soon  as  the  conditions  for  the 
chemical  reactions  in  the  egg  are  normal  again,  the 
development  may  go  on  unless  the  egg  has  suffered  by 
the  methods  used  to  prevent  development  or  by  the 
long  duration  of  the  suppression.  With  an  incomplete 
destruction  of  the  cortical  layer  both  development  as 
well  as  reversal  of  development  are  possible.  Thus  the 
writer  has  shown  that  in  the  egg  of  Arhacia  the  effect 
of  the  cortical  alteration  of  the  egg  induced  by  the 
butyric  acid  treatment  or  by  the  treatment  with  bases 
can  be  reversed.  When  unfertilized  eggs  of  Arbacia  are 
put  for  from  two  to  five  minutes  into  50  c.c.  sea  water  + 
2.0  c.c.  N/io  butyric  acid  they  will  all  form  a  gelatinous, 
somewhat  atypical  fertilization  membrane;  when  put 
back  into  normal  sea  water  all  will  perish  in  a  few  hours 
unless  they  are  submitted  to  the  short  treatment  with  a 
hypertonic  solution  mentioned  in  the  previous  chapter, 
while  if  submitted  to  this  treatment  they  will  develop. 
If,  however,  these  eggs  are  transferred  from  the  butyric 
acid  sea  water  not  into  normal  sea  water  but  into  sea 
water  containing  some  NaCN  (10  drops  of  1^0  per  cent. 
NaCN  or  KCN  in  50  c.c.  sea  water),  and  if  they  remain 
here  for  some  time  (e.  g.  overnight)  they  will  not  perish 


Regeneration  191 

when  subsequently  transferred  back  to  normal  sea  water. 
Such  eggs  will  develop  when  fertilized  with  sperm. 
The  activating  effect  of  the  membrane  formation  has, 
therefore,  been  reversed  and  the  eggs  have  gone  back 
into  the  resting  stage.  ^  Wasteneys  has  found  that  the 
rate  of  oxidation  which  was  raised  considerably  by  the 
artificial  membrane  formation  goes  back  to  the  value 
characteristic  for  the  resting  eggs  after  the  reversal 
of  their  developmental  tendency.^  Similar  results 
were  obtained  in  eggs  activated  with  NH4OH.  It 
appears  from  this  as  though  the  change  in  the  cortical 
layer  which  leads  to  the  development  of  the  egg  and 
the  increase  in  the  rate  of  oxidations  were  reversible 
in  the  egg  of  ArbaciaJ 

The  writer  had  previously  noticed  that  eggs  of 
Strongylocentrotus  purpuratus,  which  had  been  treated 
for  two  hours  with  hypertonic  sea  water,  not  infrequently 
began  to  divide  into  two,  four,  or  eight  cells  (and  some- 
times more)  and  then  went  back  into  the  resting  state 
(except  that  they  possessed  the  second  factor  required 
for  development  as  stated  in  Chapter  V).     It  may  be 

^  Loeb,  Arch.f.  EntwcUngsmech.,  1914,  xxxviii.,  277. 

"Wasteneys,  H.,  Jour.  Biol.  Chem.,  1916,  xxiv.,  281. 

3  F.  Lillie  thinks  that  the  KCN  in  this  experiment  merely  inhibits  the 
change  of  the  cortical  layer  necessary  for  development.  This  is  con- 
tradicted by  two  facts:  first,  the  writer  has  shown  in  1906  that  KCN  does 
not  inhibit  the  membrane  formation,  and,  second,  the  eggs  will  not 
return  to  the  resting  stage  when  put  back  into  sea  water  too  soon;  in 
that  case  they  will  disintegrate.  This  shows  that  in  the  KCN  something 
more  happens  than  the  mere  block  to  disintegration. 


192  Regeneration 

remarked  incidentally  that  such  eggs  at  the  time  of  cell 
division  contained  the  centrosomes  and  astrospheres, 
and  yet  went  back  into  a  resting  state^  thus  showing 
that  the  centrosomes  are  only  transitory  organs  or 
organs  which  are  only  active  under  certain  conditions. 
It  is  quite  possible  that  in  these  phenomena  of  reversal 
not  the  whole  of  the  cortical  layer  has  undergone  altera- 
tion. 

The  writer  must  leave  it  undecided  whether  the 
changes  from  the  resting  to  the  active  state  in  body 
cells  can  also  be  explained  in  analogy  with  these  experi- 
ments. 

9.  In  the  formation  of  the  lens  we  have  already 
noticed  an  instance  where  the  adjacent  organ  influences 
growth  inasmuch  as  the  optic  cup  controlled  the  for- 
mation of  the  lens.  Such  influences  are  quite  commonly 
observed.  A  piece  of  Tubularia  when  cut  out  from  a 
stem  and  suspended  in  water  will  regenerate  at  the 
aboral  pole  not  a  stolon  but  a  polyp,  so  that  we  have  an 
animal  terminating  at  both  ends  of  its  body  in  a  head. 
The  writer  called  such  cases  in  which  an  organ  is 
replaced  by  an  organ  of  a  different  kind  hetero- 
morphosis. 

Contact  with  a  salid  body  favours  the  formation  of 
stolons.  Fig.  36  shows  a  piece  of  a  stem  of  Pennaria 
another  hydroid,  which  was  lying  on  the  bottom  of  an 
aquarium  and  which  formed  stolons  at  both  ends  a  and 
b.     In  Margelis,  another  hydroid,  the  writer  observed 


Regeneration  193 

that  without  any  operation  the  apical  ends  of  branches 
which  were  in  contact  with  sohd  bodies  continued  to 
grow  as  stolons,  while  those  surrounded  by  sea  water 
continued  to  grow  as  stems. 

Herbst  discovered  a  very  interesting  form  of  hetero- 
morphosis  in  certain  crustaceans;  namely,  that  in  the 


Fig.  36 

place  of  an  eye  which  was  cut  off,  an  entirely  different 
organ  could  be  formed,  namely,  an  antenna.  He 
showed  that  the  experimenter  has  it  in  his  power  to 
determine  whether  the  crustacean  shall  regenerate  an 
eye  or  an  antenna  in  place  of  the  eye.  The  latter  will 
take  place  when  the  optic  ganglion  is  removed  with  the 
eye,  the  former  when  it  is  not  removed.  These  experi- 
ments were  carried  out  successfully  on  Palcemon, 
Palcemonetes,  Sicyonia,  Palinurus,  and  other  crus- 
taceans. 

The  influence  of  gravitation  is  very  familiar  in  plants ; 
13 


194 


Regeneration 


in  stems  of  Bryophyllum  placed  horizontally  the  roots 
usually  come  out  from  the  lower  end  of  the  callus. 
Such  phenomena  are  not  often  found  in  animals  but 
they  exist  here  too  as  the  following  observation  shows. 
If  we  cut  a  piece  a  h  (Fig.  37),  from  the  stem  ss  oi 


Fig.  37 

Antennularia  antennina  (Fig.  38),  a  hydroid,  and  put  it 
into  the  water  in  a  horizontal  position,  new  stems  cd 
(Fig.  37)  may  arise  on  its  upper  side.  The  small  branches 
on  the  under  side  of  the  old  stem  a  b  begin  suddenly  to 
grow  vertically  downward.^  In  appearance  and  func- 
tion these  downward-growing  elements  are  entirely 
different  from  the  branches  of  the  normal  Antennularia; 
they  are  roots.  In  order  to  understand  better  the 
transformation  which  thus  occurs  in  these  branches,  it 
may  be  stated  that  under  normal  conditions  they  have 


'  Loeb,    J.,    Untersuchungen   zur  physiologischen    Morphologic  der 
Tiere.  II.  Organbildung  und  Wachsthum.     Wurzburg,  1S92. 


Regeneration 


195 


Fig.  38 


a  limited  growth  (see  Fig.  38),  are  directed 
upward,  and  have  polyps  on   their  upper 
side.      The  parts  which  grow  down  (Fig. 
37)  have  no  polyps,  but  attach  themselves 
like  true  roots  to  solid  bodies.     Thus  the 
changed  position  of  the  stem  alone,  with- 
out  any    operation,  suffices  to  transform 
the    lateral    branches,    whose    growth    is 
limited,  into  roots  with  unlimited  growth. 
The  lateral  branches  on  the  upper  side  of 
the  stem  do  not  undergo  such  a  transfor- 
mation into  roots  except  in  the  immediate 
surroundings  of  the  place  where  a  new  stem 
arises.     It  seems  that  the  formation  of  a 
new  stem  also  causes  an  excessive  growth 
of  roots,  possibly  because  the  formation  of 
new  branches  causes  the  removal  of  sub- 
stances which  naturally  inhibit  the  forma- 
tion of  roots.     If  a  piece  from  the  stem  be 
put  vertically  into  the  water  with  top  down- 
ward, the  uppermost  point  may  continue 
to  grow  as  a  stem,  while  the  lowest  point 
may  give  rise  to  roots.   In  this  case,  there- 
fore, a  change  in  the  orientation  of  organs 
has  the  effect  of  changing  the  character 
of  organs. 

There  are  only  two  ways  by  which  we 
can  account  for  these  influences  of  gravi- 


196  Regeneration 

tation.  Either  certain  substances  flow  to  the  lowest 
level  and  collecting  there  induce  growth  and  possibly 
changes  in  the  character  of  growth  (as  in  Antennidaria) 
or  if  the  cells  have  elements  of  different  specific  gravity 
the  relative  position  of  these  elements  may  possibly 
change  and  influence  in  this  way  the  conditions  for 
growth.  The  influence  of  gravitation  as  well  as  of  con- 
tact upon  life  phenomena  are  at  present  httle  under- 
stood. 

In  all  these  cases  of  heteromorphosis  the  original 
form  is  not  restored.  It  is  needless  to  say  that  they  are 
incompatible  with  the  theory  of  natural  selection. 

The  reader  will  have  noticed  that  in  this  chapter  one 
term  has  not  been  mentioned  which  is  commonly  met 
with  in  the  literature,  namely  the  "wound  stimulus." 
As  the  writer  had  indicated  in  a  former  publication,^ 
the  word  "stimulus"  is  generally  used  to  disguise  our 
ignorance  of  (and  also  our  lack  of  interest  in)  the  causes 
which  underlie  the  phenomena  which  we  investigate. 
Regeneration  very  often  does  not  take  place  near  the 
wound  but  at  some  distance  from  it.  But  even  when 
the  regeneration  takes  place  at  the  edge  of  the  wound 
the  latter  only  serves  to  create  conditions  for  regen- 
eration, and  these  conditions  cannot  be  expressed  by 
the  word  "stimulus." 

While  our  knowledge  of  the  r61e  of  the  whole  in 

'  Loeb,  J.,  Die  chemische  Enlwicklungserregung  des  tierischen  Eies. 
Berlin,  1909. 


Regeneration  197 

regeneration  is  incomplete  in  a  great  many  details  it 
seems  that  the  known  facts  warrant  the  statement  that 
the  phenomena  of  regeneration  belong  as  much  to  the 
domain  of  determinism  as  those  of  any  of  the  partial 
phenomena  of  physiology. 


CHAPTER  VIII 

DETERMINATION  OF    SEX,   SECONDARY   SEXUAL   CHARAC- 
TERS, AND  SEXUAL  INSTINCTS 

/.     The  Cytological  Basis  of  Sex  Determination 

I.  It  is  a  general  fact  that  both  sexes  appear  in 
approximately  equal  numbers,  provided  a  sufficiently 
large  number  of  cases  are  examined.  This  fact  has 
furnished  the  clue  for  the  discovery  of  the  mechanism 
Vv'hich  determines  the  relative  number  of  the  two  sexes. 
The  honour  of  having  pointed  the  way  to  the  solu- 
tion of  the  problem  belongs  to  McClung.^  It  has 
been  known  that  certain  insects,  e.  g.,  Hemiptera  and 
Orthoptera,  possess  two  kinds  of  spermatozoa  but  only 
one  kind  of  eggs.  The  two  kinds  of  spermatozoa  differ 
in  regard  to  a  single  chromosome,  which  is  either  lacking 
or  different  in  one-half  of  the  spermatozoa. 

The  first  one  to  recognize  the  existence  of  two  kinds 
of  spermatozoa  was  Henking,  who  stated  that  in  Pyr- 
rhocoris   (a  Hemipteran)  one-half  of  the  spermatozoa 

'  McClung,  C.  E.,  "The  Accessory  Chromosome — Sex  Determinant?" 
Biol.  Bull.,  1902,  iii.,  43. 

198 


Basis  of  Sex  Determination  199 

of  each  male  possessed  a  nucleolus,  while  in  the  other 
half  it  was  lacking.  Montgomery  afterward  showed 
that  Henking's  nucleolus  was  an  accessory  chromosome. 
McClung  was  the  first  to  recognize  the  importance  of 
this  fact  for  the  problem  of  sex  determination.  He 
obser\^ed  an  accessory  chromosome  in  one-half  of  the 
spermatozoa  of  two  forms  of  Orthoptera,  Brachystola 
and  Hippiscus,  and  reached  the  following  conclusion: 

A  most  significant  fact,  and  one  upon  which  almost  all 
investigators  are  united  in  opinion,  is  that  the  element  is 
apportioned  to  but  one-half  of  the  spermatozoa.  Assuming 
it  to  be  true  that  the  chromatin  is  the  important  part  of  the 
cell  in  the  matter  of  heredity,  then  it  follows  that  we  have 
two  kinds  of  spermatozoa  that  differ  from  each  other  in  a 
vital  matter.  We  expect,  therefore,  to  find  in  the  offspring 
two  sorts  of  individuals  in  approximately  equal  numbers, 
under  normal  conditions,  that  exhibit  marked  differences 
in  structiu-e.  A  careful  consideration  will  suggest  that 
nothing  but  sexual  characters  thus  divides  the  members 
of  a  species  into  two  well-defined  groups,  and  we  are  logi- 
cally forced  to  the  conclusion  that  the  peculiar  chromosome 
has  some  bearing  upon  the  arrangement. 

N.  M.  Stevens  and  E.  B.  Wilson^  have  not  only 
proved  the  correctness  of  this  idea  for  a  number  of 
animals  but  have  laid  the  foundation  of  our  present 
knowledge  of  the  subject.  Wilson  showed  that  in  those 
cases  where  there  are  two  types  of  spermatozoa,  one 

^  Wilson,  E.  B.,  "Studies  on  Chromosomes, "  Jour.  Exper.  Zool.,  1905, 
ii-f  371.  507;  1906,  iii.,  i;  1909,  vi.,  69,  147;  1910,  ix.,  53;  1912,  xiii.,  345. 
"Croonian  Lecture,"  1914,  Proc.  Roy.  Soc,  B.  Ixxxviii.,  333. 


200  Basis  of  Sex  Determination 

with  and  one  without  an  accessory  or  as  it  is  now  called 
an  X  chromosome,  all  the  cells  of  the  female  have  one 
chromosome  more  than  the  cells  of  the  male.  From 
this  he  concludes  correctly  that  in  such  species  a  female 
is  produced  when  the  egg  is  fertilized  by  a  spermato- 
zoon containing  an  X  chromosome,  while  a  male  is 
produced  when  a  spermatozoon  without  an  X  chromo- 
some enters  the  egg. 

Such  a  form  is  Protenor,  one  of  the  Hemiptera.  Wilson 
made  sure  that  all  the  eggs  are  alike  in  the  number  of 
chromosomes,  each  egg  containing  an  X  chromosome  in 
addition  to  the  six  chromosomes  characteristic  of  the 
species  Protenor.  There  are  two  types  of  spermatozoa 
in  equal  numbers  in  this  species,  each  with  six  chromo- 
somes, but  one  with,  the  other  without,  an  X  chromo- 
some. The  two  possible  chromosome  combinations 
between  egg  and  spermatozoa  are  therefore  as  follows 
(see  the  diagrammatic  Fig.  39) : 

Egg  Spermatozoon  Result 

(i)  6  +  X  +6  =      12  +  X  =  Male 

(2)6  +  X  +6  +  X        =      I2  +  2X  =  Female 

The  egg  which  receives  a  spermatozoon  without  an 
X  chromosome  has  after  fertilization  12  +  X  chromo- 
somes and  develops  into  a  male;  while  the  egg  into 
which  a  spermatozoon  with  an  X  chromosome  enters 
gives  rise  to  a  female.  Since  all  the  body  cells  arise 
from  the  fertilized  egg  by  nuclear  division  and  the 


Basis  of  Sex  Determination 


20 1 


chromosomes  remain  constant  in  number  in  all  cells, 
the  consequence  is  that  all  the  cells  of  a  female  Protenor 
have  two  X  chromosomes;  while  all  the  cells  of  a  male 
Protenor  have  only  one  X  chromosome.  • 


Before  Fertilization 


Eggs 


Sperm 


After  Fertilization 
Fig.  39 


The  chromosome  situation  in  Protenor  is  a  somewhat 
extreme  case,  inasmuch  as  one  X  chromosome  is 
entirely  lacking  in  the  male.  In  other  forms  of  Hemip- 
tera,  e.  g.,  LygcBUs,  there  are  also  two  types  of  spermato- 
zoa appearing  in  equal  numbers  differing  in  regard  to 


202  Basis  of  Sex  Determination 

the  X  chromosome,  but  here  it  is  only  a  difference  in 
size ;  one-half  of  the  spermatozoa  having  a  large  X  chro- 
mosome, the  other  half  instead  a  smaller  chromosome. 
Calling  this  latter  the  Y  chromosome,  the  sex  deter- 
mination in  this  form  is  as  follows:  leaving  aside  the 
chromosomes  which  are  equal  in  both  egg  and  sperma- 
tozoon we  may  say  that  there  is  one  type  of  egg  con- 
taining one  large  X  chromosome;  there  are  two  types 
of  spermatozoa  in  equal  numbers,  one  possessing  a  large 
X  chromosome,  the  other  possessing  a  small  Y  chromo- 
some. Wilson  showed  by  a  study  of  the  chromosomes  in 
males  and  females  that  when  one  of  the  spermatozoa 
containing  a  large  X  chromosome  enters  the  egg,  the 
egg  will  develop  into  a  female;  while  when  one  of  the 
spermatozoa  containing  a  small  Y  chromosome  enters 
it  will  give  rise  to  a  male.  Leaving  aside  the  common 
chromosomes  of  both  sexes,  a  fertilized  egg  containing 
XX  gives  rise  to  a  female,  while  one  containing  XY 
gives  rise  to  a  male.  There  is  in  this  case  as  in  that  of 
Protenor  a  preponderance  of  chromosome  material  in  the 
female,  but  this  quantitative  difference  is  not  essential 
for  the  determination  of  sex,  since  in  some  species  the  Y 
chromosome  may  be  as  large  as  the  X  chromosome. 

The  main  fact  is  that  the  female  cells  have  the 
chromatin  composition  XX,  the  male  cells  the  composi- 
tion XY,  where  Y  is  apparently  qualitatively  different 
and  often,  but  not  necessarily,  smaller  than  X,  or 
entirely  lacking. 


Basis  of  Sex  Determination  203 

It  may  be  mentioned  in  passing  that  indirect  evidence 
exists  indicating  that  in  man  there  are  also  two  kinds 
of  spermatozoa  and  one  kind  of  egg,  and  that  sex 
depends  on  whether  a  male  determining  or  a  female 
determining  spermatozoon  enters  the  egg. 

2.  This  mode  of  sex  determination  holds  only  for 
those  animals  in  which  there  is  one  type  of  egg  and  two 
types  of  spermatozoa.  Experimental  evidence  furnished 
first  by  Doncaster  in  1908  on  a  moth,  Abraxas,  indi- 
cated that  a  number  of  other  forms  exists  in  which 
matters  are  reversed,  inasmuch  as  there  are  two  types 
of  eggs  and  one  type  of  spermatozoa.  This  condition  of 
affairs  exists  not  only  in  the  moth  Abraxas,  but  also 
in  the  fowl  as  shown  by  Pearl.  In  these  forms  it  is 
assumed  that  all  the  spermatozoa  have  one  sex  chromo- 
some X,  while  there  are  two  types  of  eggs,  one  possessing 
the  sex  chromosome  X,  the  other  possessing  Y.  When 
a  spermatozoon  enters  an  egg  with  an  X  chromosome, 
the  egg  will  give  rise  to  a  male,  while  if  it  enters  a  Y 
egg,  a  female  will  arise.  The  evidence  pointing  toward 
this  result  is  chiefly  contained  in  experiments  on  sex- 
limited  or  more  correctly  sex-linked  heredity;  i.  e.,  a 
form  of  heredity  which  follows  the  sex  in  a  peculiar 
way.  Thus  colour-blindness  is  a  case  of  sex-linked 
inheritance,  since  this  abnormality  appears  over- 
whelmingly in  the  male  offspring  of  a  colour-blind 
person.  Doncaster  crossed  two  varieties  oi  Abraxas  dif- 
fering in  one  character  which  was  sex-linked,  and  the 


204  Basis  of  Sex  Determination 

results  of  his  crossings  indicated  that  in  this  form  there 
are  two  types  of  eggs  and  one  type  of  spermatozoa.^ 

These  observations  on  sex-hnked  heredity  confirm 
the  idea  that  the  sex  chromosomes  determine  the  sex. 
The  most  extensive  and  conclusive  experiments  along 
this  line  are  those  by  Morgan  on  the  fruit  fly  Drosophila. 
In  this  form  there  are  two  kinds  of  spermatozoa  and 
one  kind  of  eggs;  the  egg  has  one  X  chromosome,  while 
one-half  of  the  spermatozoa  has  an  X  the  other  a  Y 
chromosome ;  the  entrance  of  the  latter  into  an  egg  gives 
rise  to  a  male,  of  the  former  to  a  female. 

While  the  eyes  of  the  wild  fruit  fly  Drosophila  ampelo- 
phila  are  red,  Morgan^  noticed  in  one  of  his  cultures 
a  male  that  had  white  eyes.  This  white-eyed  male  was 
mated  to  a  red-eyed  female.  The  offspring,  the  Fi 
generation,  were  all  red  eyed,  males  as  well  as  females. 
These  were  inbred  and  now  gave  in  the  Fj  generation 
the  following  three  types  of  offspring : 

(i)  50  per  cent,  females,  all  with  red  eyes. 

(2)  50  per  cent,  males  |  ^5  Per  cent,  with  red  eyes. 

(  25  per  cent,  with  white  eyes. 

The  character  white  eye  was  therefore  transmitted 
only  to  half  the  grandsons;  it  was  a  sex-linked  charac- 
ter. It  is  known  from  a  study  of  the  pedigrees  of 
colour-blind  individuals  that  if  the  corresponding  ex- 

'  Doncaster,  L.,  The  Determination  of  Sex.     Cambridge,  19 14. 
•  Morgan,  T.  H.,  Heredity  and  Sex.     New  York,  19 13. 


Basis  of  Sex  Determination  205 

periment  had  been  carried  out  with  them,  instead  of 
with  white-eyed  flies,  the  same  proportions  of  normal 
and  colour-bHnd  would  have  been  fotmd:  namely,  nor- 
mal colour  vision  in  the  Fi  generation,  in  both  males  and 
females,  and  half  of  the  males  of  the  F3  generation 
colour-blind,  the  other  half  and  all  the  females  with 
normal  vision.  Of  course,  in  man,  intermarriage 
between  two  different  Fi  strains  would  have  been  re- 
quired in  place  of  the  inbreeding  of  the  Fi  generation, 
which  took  place  in  Morgan's  experiments.  Morgan 
interprets  his  experiments  as  follows.  The  normal  red- 
eyed  Drosophila  has  one  kind  of  eggs,  each  possessing 
one  X  chromosome.  This  X  chromosome  has  also  the 
factor  for  the  development  of  red-eye  pigment.  The 
white-eyed  male  has  two  kinds  of  spermatozoa,  one 
with  an  X  chromosome,  the  other  with  a  Y  chromosome, 
both  lacking  the  factor  for  red-eye  pigment.  If  we 
designate  the  X  chromosome  with  the  factor  for  red- 
eye pigment  by  X  and  the  X  and  Y  chromosomes 
lacking  the  factor  for  redness  with  X  and  Y  the  follow- 
ing combinations  must  result  if  we  cross  a  normal  red- 
eyed  female  with  a  white-eyed  male; 


Eggs 

Sperm 

Result 

X 

X 

XX    red-eyed  female 

X 

Y 

XY    red-eyed  male 

It  is  obvious  that  all  the  offspring  of  the  first  genera- 
tion (the  Fi  generation)  must  be  red  eyed,  since  all  the 


2o6  Basis  of  Sex  Determination 

eggs  have  one  X  chromosome  with  the  factor  for  red. 
According  to  the  results  obtained  from  cytological 
studies  which  will  be  explained  in  the  next  chapter,  the 
females  with  the  chromatin  constitution  XX  will  form 
two  types  of  eggs  in  equal  numbers:  namely,  eggs  with 
an  X  and  eggs  with  an  X,  i.  e.,  all  eggs  have  one  X 
chromosome,  but  in  fifty  per  cent,  of  the  eggs  the  X  has 
the  factor  for  red,  in  fifty  per  cent,  this  factor  is  lack- 
ing (X).  The  males  having  the  chromosome  constitu- 
tion XY  form  two  types  of  spermatozoa,  one  with  an 
X  possessing  the  factor  for  red  pigment  and  one,  the  Y 
chromosomes,  lacking  this  factor.  If  inbred  the  next 
Fj  generation  will  give  rise  to  the  following  four  types 
of  offspring:  (i)  XX,  (2)  XX,  (3)  XY,  (4)  XY,  all  four 
types  in  equal  numbers. 

(i)  and  (2)  give  females,  both  red  eyed,  since  both 
contain  a  red-factored  X  chromosome.  (3)  and  (4) 
give  males,  (3)  giving  rise  to  red-eyed  males,  since  it 
contains  a  red-factored  X  chromosome,  (4)  producing 
males  with  white  eyes  since  this  X  chromosome  is 
lacking  the  factor  for  red  eyes.  Since  all  four  combina- 
tions must  appear  in  equal  numbers  (provided  the 
experimental  material  is  ample  enough,  which  was  the 
case  in  these  experiments),  in  the  Fi  generation  both 
males  and  females  should  have  red  eyes  and  in  the  F^ 
generation  all  the  females  should  have  red  eyes  and 
half  of  the  males  should  have  red,  half  white  eyes. 
These  results  were  obtained. 


Basis  of  Sex  Determination  207 

The  experiments  were  carried  further.  No  white-eyed 
females  had  appeared  thus  far.  On  the  same  assump- 
tions of  the  relation  of  the  X,  X,  and  Y  chromosomes  to 
the  heredity  of  sex  as  well  as  to  eye  colour  it  was 
possible  to  predict  under  what  conditions  and  in  which 
proportions  white-eyed  females  should  arise.  Thus  if 
a  red-eyed  female  of  the  F  i  generation  (a  cross  between 
white-eyed  male  and  normal  female)  be  mated  with  a 
white-eyed  male  the  result  should  be  an  equal  number 
of  white-eyed  males  and  white-eyed  females  if  the 
chromosome  theory  of  sex  determination  were  correct. 
The  reasoning  would  be  as  follows  : 

The  red-eyed  female,  having  the  chromosome  con- 
stitution XX  should  form  two  kinds  of  eggs  in  equal 
numbers  with  the  constitution  X  and  X;  the  white- 
eyed  male  having  the  chromosome  constitution  XY 
should  form  two  kinds  of  spermatozoa  X  and  Y.  The 
following  four  types  of  individuals  must  then  be  pro- 
duced in  equal  numbers : 

(I)  XX,  (2)  XX,  (3)  XY,  and  (4)  XY. 

In  this  case  (2)  must  give  rise  to  white-eyed  females 
and  (4)  to  white-eyed  males,  while  (i)  must  give  rise 
to  red-eyed  females  and  (3)  to  red-eyed  males.  Hence 
white-eyed  males  and  females  and  red-eyed  males  and 
females  are  to  be  expected  in  this  case  in  equal  num- 
bers, and  this  was  actually  observed. 

The  numerical   agreement   in   this   and   the   other 


2o8  Basis  of  Sex  Determination 

experiments  between  the  expected  and  observed  result 
cannot  well  be  an  accident.  The  fact  that  the  inheri- 
tance of  sex-linked  characters  in  man  follows  the  same 
laws  as  in  Drosophila  is  a  strong  argument  in  favour  of 
the  assumption  that  in  man,  also,  sex  is  determined  by 
two  kinds  of  spermatozoa. 

Morgan  and  his  students  discovered  no  less  than 
thirty-six  sex-linked  characters  in  Drosophila,  and  each 
behaved  in  a  similar  way  to  the  red  and  white  eye 
colour  in  regard  to  sex-linked  inheritance,  so  that  the 
chromosome  theory  of  sex  determination  rests  on  a  safe 
basis.  That  sex  is  merely  determined  by  the  number 
of  X  chromosomes,  not  by  the  Y  chromosome,  is  proved 
by  the  facts  that  the  Y  chromosome  may  be  completely 
absent  as  in  Protenor  and  that  Bridges^  has  found  a 
type  of  female  Drosophila  with  a  chromosome  formula 
XXY  whose  sex  was  not  affected  by  the  supernu- 
merary Y. 

3.  On  the  basis  of  all  these  experiments  and  theories 
it  is  comparatively  easy  to  explain  a  number  of  pheno- 
mena concerning  sex  ratios  which  before  had  been  very 
puzzling.  In  bees  it  had  been  shown  many  years  ago 
by  Dzierzon  that  the  males  develop  from  unfertilized 
eggs  while  the  females,  queens  and  workers,  develop 
from  fertilized  eggs.  This  is  intelligible  on  the  assump- 
tion that  the  unfertilized  egg  contains  only  one  X 
chromosome  while  the  spermatozoon  carries  into  the 

'Bridges,  C.  B.,  Genetics,  19 16,  i.,  i. 


Basis  of  Sex  Determination  209 

egg  the  second  X  chromosome.  But  if  the  male  bee  pro- 
duces two  types  of  spermatozoa  we  should  expect  that 
only  one-half  of  the  fertilized  eggs  should  be  females, 
the  other  half  males.  But  it  happens  that  of  the  two 
types  of  spermatozoa  only  one  is  formed  since  in  one  of 
the  cell  divisions  which  lead  to  the  formation  of  sperma- 
tozoa one  viable  spermatozoon  only  is  formed  while 
the  other  one  perishes.  It  is,  therefore,  quite  pos- 
sible that  it  is  the  female-producing  spermatozoon 
which  survives  while  the  male-producing  spermatozoon 
dies. 

It  is  occasionally  observed  that  an  insect  shows  one 
sex  on  one  side  of  its  body  and  the  opposite  sex  on  the 
other  side.  Boveri  suggested  that  this  phenomenon  of 
gynandromorphism  is  due  to  the  fact  that  the  spermato- 
zoon for  some  unknown  reason  does  not  fuse  with  the 
egg  nucleus  until  after  the  egg  has  m'ldergone  its  first 
cell  division.  In  this  case  it  fuses  with  the  nucleus  of  one 
of  the  two  cells  into  which  the  egg  divides  (or  in  some 
cases  even  one  of  the  later  cells?).  As  a  consequence 
the  one-half  of  the  embryo  which  arises  from  the  cell 
which  was  not  fertilized  would  have  only  one  X  chromo- 
some and  in  a  case  like  the  bee  would  develop  par- 
thenogenetically,  while  the  other  half  of  the  body, 
developing  from  the  cell  into  which  a  spermatozoon 
has  penetrated,  would  be  fertilized.  The  latter  half 
of  the  body  would  be  female,  the  former  male.  In  his 
last  paper  before  his  imtimely  death,  Boveri  has  given 

14 


210  Basis  of  Sex  Determination 

proof  for  the  correctness  of  this  interpretation  as  far  as 
gynandromorphism  in  the  bee  is  concerned.^ 

It  seems  to  be  generally  true  that  where  sexual 
reproduction  leads  only  to  the  formation  of  females 
the  case  finds  its  explanation  in  the  fact  that  the 
male-producing  spermatozoa  perish  and  only  the 
female-producing  spermatozoa  survive.  Such  an  ob- 
servation was  made  by  Morgan  on  a  certain  species 
of  phylloxerans. 

The  slight  preponderance  in  the  number  of  one  sex 
which  is  occasionally  found — an  excess  of  six  per  cent, 
males  over  females  in  the  human  race — may  well  find 
its  explanation  on  the  assumption  of  a  slightly  greater 
mortality  of  the  female-determining  spermatozoa. 

In  certain  forms  parthenogenetic  and  sexual  reproduc- 
tion may  alternate  in  a  cycle,  e.  g.,  in  plant  lice,  Daphnia^ 
and  rotifers.  In  plant  lice  it  has  been  observed  for  a 
long  time  that  when  the  plant  is  normal  and  the  weather 
warm  the  aphides  remain  wingless,  reproduce  par- 
thenogenetically,  and  only  females  exist,  and  this  may 
last  for  years  and  for  more  than  fifty  generations ;  but 
that  when  the  plant  is  allowed  to  dry  out  both  sexes 
appear. 

Here  we  are  dealing  with  a  limited  determination  of 
sex  inasmuch  as  the  experimenter  has  it  in  his  power  to 
prevent  or  allow  the  production  of  males.  The  facts 
do  not  in  all  probability   contradict    the   statements 

*  Boveri,  Th.,  Arch.f.  Entwcklngsmech.,  1915,  xlii.,  264. 


Basis  of  Sex  Determination  211 

made  concerning  the  role  of  the  X  chromosomes  in  the 
determination  of  sex.  "We  have  seen  that  where  sex  is 
determined  by  two  types  of  spermatozoa  one  type  of 
eggs  is  produced  which  possesses  only  one  X  chromo- 
some. Such  eggs  might  produce  males  if  not  fertilized 
(as  they  do  in  bees),  but  they  cannot  produce  females 
because  for  that  purpose  they  must  have  two  X  chromo- 
somes. It  has  been  shown  for  certain  cases,  and  it  may 
be  true  generally,  that  if  eggs  of  this  type  give  rise  to 
parthenogenetic  females  they  may  do  so  because  they 
have  for  some  reason  two  X  chromosomes.  Usually 
such  an  egg  loses  one  of  the  X  chromosom.es  in  a  process 
of  nuclear  division  (the  so-called  reduction  division) 
which  usually  precedes  fertilization.  If  this  reduction 
division  is  omitted  the  egg  has  two  X  chromosomes  and 
if  such  an  egg  develops  parthenogenetically  it  gives  rise 
to  a  female.  These  cases  do  not,  therefore,  contradict 
the  connection  between  X  chromosomes  and  sex  deter- 
mination established  by  cytological  observations  and 
breeding  experiments,  on  the  contrar>^  they  confirm  it. 
The  question  remains:  How  can  external  conditions 
bring  it  about  that  the  reduction  division  is  omitted? 
To  this  question  no  definite  answer  can  be  given  at 
present. 

We  may  in  passing  mention  the  weU-known  observa- 
tion that  twins  which  originate  from  the  same  egg 
always  have  the  same  sex;  while  twins  arising  from 
different  eggs  show  the  usual  variation  as  to  sex.    Twins 


212  Basis  of  Sex  Determination 

I  - 
coming  from  one  egg  have  the  same  chorion  and  can 

thereby  be  diagnosed  as  such.  They  can  be  produced 
as  we  have  stated  in  Chapter  V  by  a  separation  of  the 
first  two  cleavage  cells  of  the  egg,  each  one  giving  rise 
to  a  full  embryo.  It  harmonizes  with  all  that  has  been 
said  above  that  fhe  sex  of  two  such  individuals  must 
be  the  same  since  tuej  -lave  the  same  number  of  X 
chromosomes,  the  latter  being  determined  in  the  human 
race  by  the  nature  of  the  spermatozoon  which  enters 
the  egg. 

4.  While  thus  far  all  the  facts  agree  with  the 
dominating  influence  of  certain  chromosomes  upon 
sex  determination,  one  group  of  facts  has  not  yet  been 
explained:  namely,  hermaphroditism.  By  hermaphro- 
ditism is  meant  the  existence  of  complete  and  separate 
sets  of  female  and  male  gonads  in  the  same  individual. 
This  condition  exists  regularly  not  only  in  definite 
groups  of  animals,  e.  g.,  certain  snails,  leeches,  tape- 
worms, but  also,  as  everybody  knows,  in  flowering 
plants.  While  in  some  forms  both  kinds  of  sex  cells, 
male  and  female,  are  formed  and  mature  simultaneously, 
as,  e.  g.,  in  the  Ascidian  Ciona  (see  Chapter  IV),  in  others 
they  are  formed  successively,  very  often  the  sperma- 
tozoa appearing  first  (protandric  hermaphroditism). 
In  the  long  tapeworm  TcBuia  each  ring  has  testes 
and  ovaries,  but  the  young  rings  are  only  male  while 
in  the  older  rings  the  testes  disappear  and  the  ovaries 
are  formed.    The  same  ring  is  in  succession  male  and 


Basis  of  Sex  Determination  213 

female.  How  can  we  reconcile  the  facts  of  hermaphro- 
ditism with  the  chromosome  theory  of  sex  determina- 
tion? Bkahdonema  nigrovenosum,  a  parasite  living  in 
the  lungs  of  the  frog,  is  hermaphroditic,  but  its  eggs 
produce  not  a  hermaphroditic  generation  but  one  with 
the  two  separate  sexes;  this  generation  is  not  parasitic 
and  lives  in  the  soil.  The  generation  produced  by  these 
separate  males  and  females  gives  rise  again  to  a  her- 
maphrodite which  migrates  into  the  lungs  of  the  frogs. 
According  to  Boveri  and  Schleip'  the  cells  of  the  her- 
maphrodite have  twelve  chromosomes.  It  produces  two 
types  of  spermatozoa  with  six  and  five  chromosomes 
respectively  (one-half  of  the  cells  losing  one  chromosome 
which  is  left  at  the  line  of  cleavage  between  the  two 
cells) ;  and  one  type  with  six  chromosomes.  In  this  way 
separate  males  and  females  are  produced  by  the  her- 
maphrodite, females  with  twelve  and  males  with  eleven 
chromosomes. 

The  males  produce  again  two  kinds  of  spermatozoa, 
male  and  female  producing,  but  the  male-producing 
spermatozoa  become  functionless.  This  fusion  of  the 
other  spermatozoon  containing  six  chromosomes  with 
an  egg  having  six  chromosomes  leads  again  to  the  for- 
mation of  the  hermaphrodite  with  twelve  chromosomes. 
It  is  obvious  that  in  this  case  the  cause  for  the  her- 
maphroditism is  not  disclosed.     If  chromosomes  have 

'Boveri,  Th.,  Verhand.  d.  phys.-med.  GesellscJt.  Wurzburg,  191 1, 
xli.,  85.     Schleip,  W.,  Ber.  d.  naturf.  Gesellsch.,  Freiburg  i.  Br.,  191 1,  xix. 


214  Basis  of  Sex  Determination 

anything  to  do  with  hermaphroditism  there  must  be  an 
undiscovered  element  in  the  chromosomes  which  may 
explain  why  the  female  as  well  as  the  hermaphrodite 
have  the  same  chromosome  constitution;  or  we  are 
forced  to  look  for  another  determinant  outside  the  X 
chromosomes  or  the  chromosomes  altogether.  This 
seems  to  be  the  only  cytological  work  on  the  problem  of 
hermaphroditism.  Experimental  work  has  been  begun 
by  Correns^  and  by  ShuU  on  the  determination  of 
hermaphroditism  in  plants  but  lack  of  space  forbids  us 
to  give  details. 

II.     The  Physiological  Basis  of  Sex  Determination 

5.  As  stated  at  the  beginning  of  this  chapter,  the 
chromosome  theory  of  sex  determination  explained 
only  one  feature  of  the  problem,  namely,  the  relative 
numbers  in  which  both  sexes  or  only  one  sex,  as  the  case 
may  be,  are  produced ;  and  in  this  respect  the  evidence  is 
so  complete  that  we  must  accept  it.  But  with  all  this, 
the  problem  of  sex  determination  is  not  exhausted, 
since  a  physiological  solution  of  the  problem  of  sex 
determination  demands  an  account  of  how  the  sex 
chromosomes  can  induce  the  formation  not  only  of 
ovaries  and  testes  but  also  of  the  other  sex  characters. 
For  the  solution  of  this  problem  biology  will  have  to 
depend  largely  on  experiments  in  which  it  is  possible 

'  Correns,  C,  Biol.  Centralbl.,  1916,  xxxvi.,  12. 


Basis  of  Sex  Determination 


21: 


to  influence  the  formation  of  sex  characters  and  of  the 
sex  glands  themselves. 

The  most  striking  observations  in  this  direction 
were  made  by  Baltzer  on  a  marine  worm,  Bonellia.  In 
this  animal  the  two  sexes  are  very  different,  the  male 
being  a  tiny  parasite,  a  few  millimetres  in  length,  which 
spends  its  life  in  the  uterus  of  the  female,  whose  size  is 
about  five  centimetres.  A  female  carries  as  a  rule 
several  and  often  a  large  number  of  the  male  parasites 
in  its  uterus,  which  indicates  that  the  males  prevail 
numerically.  The  fertilized  eggs  of  the  animals  are 
laid  in  the  sea  water  where  the  larvs  hatch.  At  the 
time  of  hatching  all  larvae  are  alike.  The  differentiation 
of  the  larvce  into  the  dwarf  males  and  the  giant  females 
can  be  determined  at  will.  The  larv^  have  a  tendency 
to  attach  themselves  to  the  proboscis  of  the  female  as 
soon  as  they  hatch.  If  given  a  chance  to  do  so  and  if 
they  stick  to  the  proboscis  for  more  than  three  days  they 
will  develop  into  males,  which  soon  afterwards  creep 
into  the  female  where  they  continue  their  parasitic 
existence.  If,  however,  no  adult  female  Bonellia  is  put 
into  the  aquarium  in  which  the  larvae  hatch,  about 
ninety  per  cent,  of  the  larvae  will,  after  a  period  of  rest, 
develop  into  females;  the  rest  develop  into  males. 
Those  which  develop  into  females  will  often  show  a 
primary  maleness  which  may  manifest  itself  in  the  pro- 
duction of  sperm  or  of  other  secondary  male  sexual 
characters.     This  tendency  is  stronger  the  longer  the 


2i6  Basis  of  Sex  Determination 

period  of  rest  lasts.  If  the  larvae  are  allowed  to  settle 
on  the  proboscis  of  the  adult  female  but  are  removed 
too  early  hermaphrodites  are  produced  having  male  and 
female  characters  mixed. 

Baltzer  has  suggested  on  the  basis  of  some  observa- 
tions that  the  larvse  while  on  the  proboscis  of  the  female 
absorb  some  substance  secreted  by  the  proboscis,  and 
this  substance  accelerates  the  further  development 
into  a  male  and  suppresses  the  female  tendency.  If 
this  substance  from  the  proboscis  does  not  reach  the 
larvae  the  tendency  to  become  males  is  gradually 
suppressed  in  the  majority  and  only  a  few  develop  into 
pure  males  or  protandric  hermaphrodites,  while  the 
female  characters  are  given  a  chance  to  develop. 
Baltzer  assumes,  therefore, — as  it  seems  to  us  correctly 
— that  in  all  larvae  the  tendency  for  both  sexual  char- 
acters is  present,  that  they  are,  in  other  words,  herma- 
phrodites, but  the  chance  for  the  suppression  of  one 
and  the  development  of  the  other  group  of  characters 
can  be  influenced  by  certain  chemical  substances  which 
the  larva  may  take  up.  ^ 

Giard  has  studied  the  effects  of  a  curious  form  of  cas- 
tration brought  about  by  parasites,  which  is  followed 
by  a  change  in  the  sexual  character  of  the  castrated 
animal.  The  phenomenon  is  very  striking  in  certain 
forms  of  crabs  when  they  are  attacked  by  a  parasitic 
crustacean,  Sacculina.     The  two  sexes  differ  in  the  crab 

» Baltzer,  F.,  Mitteil.  d.  zoolog.  Station,  Neapel,  1914,  xxii. 


Basis  of  Sex  Determination  217 

Carcinus  mcenas  by  the  form  of  the  abdomen,  but  when 
a  male  is  attacked  by  the  parasite  its  abdomen  assumes 
the  female  shape.  Smith  observed  in  another  crab 
that  in  such  cases  even  the  abdominal  appendages  of  the 
male  may  be  transformed  into  those  of  a  female.  The 
transformation  is  so  complete  that  the  older  observers 
had  reached  the  conclusion  that  the  parasite  attacked 
only  the  females,  since  they  overlooked  the  fact  that 
the  castration  by  the  parasite  transformed  the  sec- 
ondary sexual  characters  of  the  male  into  those  of  a 
female. 

Giard  observed  that  in  a  dioecious  plant,  Lychnis 
diotca,  a  parasitic  fungus  brings  about  the  transfor- 
mation of  the  host  into  a  hermaphrodite. 

G.  Smith  has  discovered  a  fact  which  shows  that 
chemical  changes  must  underhe  these  morphological 
transformations  of  primary  or  secondary  sexual  char- 
acters. He  noticed  that  in  male  crabs  the  presence  of 
the  parasite  Sacculina  changes  the  contents  of  the 
fatty  constituents  in  the  blood,  making  them  equal 
to  that  of  the  female.  Vaney  and  Meignon  had  pre- 
viously shown  that  during  the  chrysalid  stage  the  female 
silkworms  have  always  more  glycogen  and  less  fat  than 
the  males.  The  castration  by  parasites  is  paralleled 
by  what  Caullery  calls  the  castration  by  seniHty.* 
In  certain  birds  and  also  in  mammals  at  the  time  when 
the  sexual  glands  cease  to  function  certain  secondary 

'Caullery,  M,,  Les  Prohlemes  de  la  Sexualite.     Paris,  1913. 


2i8  Basis  of  Sex  Determination 

sexual  characters  of  the  other  sex  make  their  appear- 
ance. The  most  common  case  is  that  certain  secondary 
male  characters  appear  in  the  old  female  (exceptionally 
also  in  the  young  female  with  abnormal  ovaries) 
(arrhenoidy).  Thus  old  female  pheasants  assume  the 
plumage  of  the  male,  and  in  the  human  female  after 
the  menopause  and  especially  among  sterile  women  a 
beard  may  begin  to  grow.  The  opposite  phenomenon, 
the  old  male  assuming  female  characters,  is  not  so 
common.  Very  interesting  observations  on  changes 
in  the  plumage  of  castrated  fowl  have  recently  been 
made  by  Goodale.  ^ 

It  had  long  been  observed  by  cattle  breeders  that  in 
the  case  of  twins  of  different  sex  the  female — the 
so-called  free-martin — is  usually  sterile.  F.  Lillie*  has 
recently  discovered  the  cause  of  this  interesting 
phenomenon.  Such  twins  originate  from  two  different 
eggs  since  the  mother  has  two  corpora  lutea,  one  in 
each  ovary.  In  normal  single  pregnancies  in  cattle 
there  is  never  more  than  one  corpus  luteum  present. 
The  two  eggs  begin  to  develop  separately  in  each  horn 
of  the  uterus. 

The  rapidly  elongating  ova  meet  and  fuse  in  the  small 
body  of  the  uterus  at  some  time  between  the  lo  mm.  and 
the  20  mm.  stage.  The  blood-vessels  from  each  side  then 
anastomose  in  the  connecting  part  of  the  chorion;  a  par- 
ticularly wide  arterial  anastomosis  develops,  so  that  either 

'  Goodale,  H.  D.,  Biol.  Bull,  1916,  xxx.,  286. 

'  Lillie,  F.,  Science,  1916,  xliii.,  611. 


Basis  of  Sex  Determination  219 

fetus  can  be  injected  from  the  other.  The  arterial  circula- 
tion of  each  also  overlaps  the  venous  territory  of  the  other, 
so  that  a  constant  interchange  of  blood  takes  place.  If 
both  are  males  or  both  are  females  no  harm  results  from 
this ;  but  if  one  is  male  and  the  other  female,  the  reproductive 
system  of  the  female  is  largely  suppressed,  and  certain  male 
organs  even  develop  in  the  female.  This  is  unquestionably  to 
be  interpreted  as  a  case  of  hormone  action. 

The  reproductive  system  of  these  sterile  females  is  for 
the  most  part  of  the  female  type,  though  greatly  reduced. 
The  gonad  is  the  part  most  affected ;  so  much  so  that  most 
authors  have  interpreted  it  as  testis. 

It  should  be  added,  however,  that  this  result  cannot 
at  present  be  generalized,  since  in  the  hermaphrodites 
the  specific  hormones  of  both  sexes  must  circulate 
without  suppressing  each  other's  efficiency. 

All  these  facts  indicate  that  certain  substances 
secreted  by  the  ovaries  or  testes  may  inhibit  the  de- 
velopment of  certain  sexual  characters  of  the  opposite 
sex.  When  these  inhibitions  are  partly  or  entirely 
removed  the  secondary  sexual  characters  of  the  opposite 
sex  may  appear.  This  fact  may  also  be  interpreted  as 
an  indication  of  a  latent  hermaphroditism  and  if  this 
be  correct  the  real  and  latent  hermaphrodites  differ 
only  by  the  degree  of  inhibition  for  one  sex,  this  inhibi- 
tion being  lacking  or  less  complete  in  the  real  than  in 
the  latent  hermaphrodite. 

In  the  light  of  this  conclusion  the  observations  on 
the  regeneration  of  both  ovaries  and  testicles  which 
Janda  observed  in  a  hermaphroditic  worm,  Criodrilus 


220  Basis  of  Sex  Determination 

lacuum,  ^  is  no  longer  so  mysterious.  This  worm  nor- 
mally possesses  in  the  segments  near  the  head  a  pair  of 
ovaries  and  several  pairs  of  testes.  Janda  found  that  if 
the  anterior  parts  containing  the  gonads  of  these  worms 
are  cut  off  a  complete  regeneration  takes  place,  includ- 
ing both  types  of  gonads,  ovaries  as  well  as  testes.  As 
a  rule,  more  than  one  pair  of  ovaries  appear  in  the 
regenerated  piece.  This  important  experiment  shows 
that  in  a  hermaphrodite  both  types  of  sex  organs 
can  be  produced  from  body  cells  or  from  latent  buds 
resembling  body  cells.  This  phenomenon  would  be 
intelligible  on  the  assumption  that  in  the  body  of  a 
hermaphrodite  substances  circulate  which  favour  the 
development  of  both  types  of  sex  organs,  while  in  a 
dioecian  animal  probably  only  one  type  of  sex  organ 
would  be  developed;  the  formation  of  the  other  being 
inhibited. 

Richard  Goldschmidt  has  discovered  in  his  breeding 
experiments  on  the  gipsy-moth  {Lymanlria  dispar) 
a  phenomenon  which  will  probably  throw  much  light 
on  the  physiology  of  sex  determination.  He  found 
that  certain  crosses  between  the  Japanese  and  the 
European  gipsy-moth  do  not  give  pure  sexes,  males  or 
females,  but  mixtures  of  the  sexual  characters  of  both 
sexes,  and. this  mixture  is  a  very  definite  one  for  defin- 
ite crosses*  These  differences  are  such  that  it  is 
possible  to  grade  the  hybrids  according  to  their  mani- 

'  Janda,  V.,  Arch.  f.  Enlwcklngsmech.,  1912,  xxxiii.,  345;  xxxiv.,  557. 


Basis  of  Sex  Determination  221 

festations  of  maleness  or  femaleness,  both  in  mor- 
phological characters  and  instincts.  Goldschmidt  calls 
this  peculiar  phenomenon  intersexualism,  and  its 
essential  feature  is  that  the  various  degrees  of  inter- 
sexualism can  be  produced  at  will  by  the  right 
combination  of  races. 

Female  intersexualism  begins  with  animals  which  show 
feathered  antenna  of  medium  size  (feathered  antennas 
are  a  male  character),  but  which  are  otherwise  entirely 
female  in  appearance  except  that  they  produce  a  smaller 
number  of  eggs  which  are  fertilized  normally.  In  the  next 
stage  patches  of  the  brown  male  pigment  appear  on  the 
white  female  wings  in  steadily  increasing  quantity.  The 
instincts  are  still  female,  the  males  are  attracted  and 
copulate.  But  the  characteristic  egg  sponge  laid  by  the 
animal  contains  nothing  but  anal  hairs  in  spite  of  the  fact 
that  the  abdomen  is  filled  with  ripe  eggs.  In  the  next  stage 
whole  sections  of  the  wings  show  male  colotuation,  with 
cuneiform  female  sectors  between,  the  abdomen  becomes 
smaller,  contains  fewer  ripe  eggs,  the  instincts  are  only 
slightly  female,  the  males  are  attracted  very  little,  and  re- 
production is  impossible.  In  the  next  stage  the  male 
pigment  covers  practically  the  whole  wing,  the  abdomen 
is  almost  male,  but  still  contains  ovaries  with  a  few  ripe 
eggs,  the  instincts  are  intermediate  between  male  and 
female.  Then  follow  very  male-like  animals  which  still 
show  in  different  organs  their  female  origin  and  have  rudi- 
mentary ovaries.  .  .  .  The  end  of  the  series  is  formed  by 
males,  which  show  in  some  minor  characters,  such  as 
the  shape  of  wings,  still  some  traces  of  their  female  origin. 

The  series  of  the  male  intersexes  starts  with  males  show- 
ing a  few  white  female  spots  on  their  wings.  These  be- 
come larger  and  larger,   the  amotuit  of  brown  pigment 


222  Basis  of  Sex  Determination 

correspondingly  decreasing.  .  .  .  Hand  in  hand  with  this 
the  abdomen  increases  in  size,  reaching  in  the  most  extreme 
cases  two-thirds  of  the  female  size  (without  containing 
eggs).  The  same  is  true  for  the  instincts  which  become 
more  and  more  female. 

(And  also  for  the  copulatory  organs  which  also  become 
more  and  more  female.) 

As  stated  above,  the  main  fact  that  every  desired 
degree  of  intersexualism  can  be  produced  at  will  by 
properly  combining  the  races  for  breeding,  and  the 
intersexual  potencies  of  the  different  races  has  been 
worked  out  by  Goldschmidt.^ 

6.  The  relation  between  chemical  substances  cir- 
culating in  the  body — either  derivatives  of  food  taken 
up  from  without  or  of  chemical  compounds  formed 
naturally  inside  the  body — and  the  production  of 
sexual  characters  is  best  shown  in  the  polymorphism 
found  among  the  social  ants,  bees,  and  wasps.  Here  we 
have,  as  a  rule,  in  addition  to  the  two  sexes  a  third 
one,  the  workers,  which  are  in  reality  rudimentary 
and  for  that  reason  sterile  females.  They  differ  more  or 
less  markedly  from  both  the  typical  male  and  female 
in  their  external  form,  and,  as  a  rule  cannot  copulate 
owing  to  their  deficient  structure.  This  third  sex, 
the  sterile  neuters,  can  be  transformed  at  desire  into 
sexual  females  in  certain  species,  as  P.  Marchal  has 
demonstrated.     He  worked  with  a  form  of  social  wasps 

'  Goldschmidt,  R.,  Proc.  Nat.  Acad.  Sc,  1916,  ii.,  53;  Ztschr.  induct. 
Abslammungslehre,  1912,  vii.,  and  1914,  xi. 


Basis  of  Sex  Determination  223 

in  which  the  workers  are  sterile  and  smaller  than  the 
real  females.  In  such  a  society  of  wasps  all  the  males 
and  workers  die  in  the  fall  and  only  the  fertilized 
females  survive,  each  one  founding  a  new  nest  in  the 
following  spring.  From  the  first  eggs  laid,  workers 
arise,  small  in  stature  and  sterile;  these  workers  are 
nourished  by  their  mother.  Then  these  workers  take 
care  of  the  feeding  of  all  those  larvee  which  arise  from 
the  eggs  which  their  mother  continues  to  lay.  Through- 
out the  spring  only  workers  arise  from  the  eggs.  The 
males  appear  in  the  summer,  the  real  females  towards 
the  end  of  the  season  when  the  sexes  copulate. 

Marchal  isolated  a  number  of  the  sterile  workers, 
providing  them  with  food  but  giving  them  no  larv£e 
to  raise.  He  found  that  the  workers  which  thus  far 
had  been  sterile  became  fertile,  producing,  however, 
only  males.  This  latter  fact  is  easily  understood  from 
what  has  been  said  regarding  the  bees,  namely,  that 
the  female  produces  only  one  type  of  eggs,  hence  the 
unfertiHzed  egg  can  give  rise  only  to  males.  The 
astonishing  or  important  point  is  that  the  ovaries  of 
the  workers  begin  to  develop  as  soon  as  they  no  longer 
have  a  chance  to  nourish  the  larvae,  provided  the  food 
which  would  have  been  given  to  the  larvae  is  now  at 
their  disposal.  In  other  words,  the  development  of 
their  ovaries  is  the  outcome  of  eating  the  food  which 
under  normal  conditions  they  would  have  given  to  the 
larvse.     The  food  must,  therefore,  contain  a  substance 


224  Basis  of  Sex  Determination 

which  induces  the  development  of  eggs.  The  natural 
sterility  of  the  neuters  or  workers  is,  therefore,  to  use 
P.  Alarchal's  expression,  a  case  of  "food  castration," 
("castration  nutriciale ") ,  ^  The  workers  originate 
from  fertilized  eggs  and  are  therefore  females,  but  for 
the  full  development  of  the  ovaries  and  the  other 
sexual  characters  something  else  besides  the  XX 
chromosomes  is  needed  and  this  is  supplied  in  this  case 
by  the  quantity  or  quality  of  the  food.  May  we  not 
conclude  that  the  same  thing  may  happen  generally, 
except  that  these  substances  are  formed  by  the  body 
under  the  normal  conditions  of  nutrition  through  the 
influence  of  constituents  of  the  second  X  chromosome? 

It  is  known  that  the  future  queens  among  the  bees 
receive  also  a  special  type  of  food  which  the  workers  do 
not  receive.  Again  the  idea  of  "food  castration"  of 
the  latter  is  suggested. 

In  rotifers  Whitney^  has  shown  that  the  cycle  in  the 
production  of  males  and  females  can  be  regulated  by 
the  food.  In  some  species  a  scanty  supply  of  green 
flagellates  produced  purely  female  offspring,  while  a 
copious  diet  of  the  same  green  flagellates  produced  a 
predominance  of  male  grandchildren,  sometimes  as  high 
as  ninety-five  per  cent.  This  was  confirmed  by  Shull 
and  Ladoff.3 

^This  account  of  Marchal's  beautiful  experiments    is    taken  from 
Caullery,  M.,  Les  Problemes  de  la  Sexualile.     Paris,  1913. 
^Whitney,  D.  D.,  Science,  1916,  xliii.,  176.    . 
3  Shull,  A.  F.,  and  Ladoff,  S.,  Science,  1916,  xliii.,  177. 


Basis  of  Sex  Determination  225 

7.  The  effects  of  the  removal  of  the  ovaries  or 
testes  upon  the  development  of  secondary  sexual 
characters  differ  for  different  species.  In  insects  the 
secondary  sexual  characters  are  not  altered  by  an 
operative  removal  of  the  sexual  glands  as  in  the  cater- 
pillar, e.  g.,  Ocneria  dispar,  according  to  Oudemans. 
This  result  has  been  invariably  confirmed  by  all  subse- 
quent workers,  especially  by  Meisenheimer.  Crampton 
grafted  the  heads  of  pup^  of  butterflies  upon  the  bodies 
of  other  specimens  of  the  opposite  sex,  but  the  sexual 
characters  of  the  head  remained  imaltered. 

In  vertebrates,  however,  there  exists  a  distinct 
influence  of  a  secretion  from  the  sexual  glands  upon  the 
development  of  certain  of  the  secondary  sexual  char- 
acters, which  do  not  develop  until  sexual  maturity. 
In  a  way  the  observations  on  arrhenoidy  and  thelyidy 
referred  to  above  are  indications  of  this  influence. 

Bouin  and  Ancel  had  already  suggested  that  the 
sexual  glands  of  mammals  have  two  independent 
constituents,  the  sexual  cells  and  the  interstitial  tissue; 
and  that  the  latter  tissue  is  responsible  for  the  develop- 
ment of  the  secondary  sexual  character.  This  has 
been  proved  definitely  by  Steinach,^  who  showed  that 
when  young  rats  are  castrated  certain  secondary 
sexual  characters  are  not  fully  developed.  The  seminal 
vesicles    and    the   prostate    remain    rudimentary  and 

'  Steinach,  E.,  Zentralhl.  f.  Physiol.,  1910,  xxiv.,  551;  Arch.  f.  d.ges, 
Physiol.,  1912,  cxliv.,  72. 


226  Basis  of  Sex  Determination 

the  penis  develops  incompletely.  Such  animals  when 
adult  recognize  the  female  and  seem  to  follow  it,  but 
do  not  persist  in  their  attention  and  neither  erection 
nor  cohabitation  occurs.  When,  however,  the  testes 
are  retransplanted  into  the  muscles  of  the  castrated 
young  animal  (so  that  they  are  no  longer  connected 
with  their  nerves)  seminal  vesicles,  prostate,  and  penis 
develop  normally,  and  these  animals  show  normal 
sexual  ardour  and  cohabitate  with  a  female  although  the 
female  cannot  become  pregnant  since  the  males  cannot 
ejaculate  any  sperm.  When  the  retransplanted  testes 
were  examined  it  was  found  that  all  the  sperm  cells 
had  perished,  only  the  interstitial  tissue  of  the  testes 
remaining.  It  was,  therefore,  proved  that  the  develop- 
ment of  the  seminal  vesicles,  the  prostate,  the  penis, 
and  the  normal  sexual  instincts  and  activities  depends 
upon  the  internal  secretions  from  this  interstitial  tissue 
and  not  upon  the  sex  cells  proper.  This  agrees  with  the 
conclusions  at  which  Bouin  and  Ancel  had  arrived  by 
ligaturing  the  vasa  deferentia  of  male  animals. 

Steinach  in  another  series  of  experiments  castrated 
young  male  rats  and  transplanted  into  them  the  ovaries 
of  young  females.  These  ovaries  did  not  disintegrate, 
the  eggs  remaining,  and  corpora  lutea  were  formed. 
In  such  feminized  individuals  the  seminal  vesicles, 
prostate,  and  penis  did  not  reach  their  normal  develop- 
ment, and  it  was  thereby  proved  that  the  internal  secre- 
tions from  the  ovary  do  not  promote  the  growth  of  the 


Basis  of  Sex  Determination  22^ 

secondary  sexual  male  characters.  On  the  contrary, 
Steinach  was  able  to  show  that  the  growth  of  the 
penis  was  directly  inhibited  by  the  ovary,  since  in  the 
feminized  males  this  organ  remained  smaller  than  in 
the  merely  castrated  animals.  On  the  other  hand  the 
infantile  uterus  and  tube  when  transplanted  into  the 
young  male  with  the  ovaries  grow  in  a  normal  way, 
and  Steinach  thinks  that  pregnancy  in  such  feminized 
males  is  possible  if  sperm  be  injected  into  the  uterus. 
In  some  regards  the  feminized  males  showed  the  mor- 
phological habitus  of  females.  Soon  after  the  trans- 
plantation of  ovaries  into  a  castrated  male  the  nipples 
of  its  mammary  glands  begin  to  grow  to  the  large  size 
which  they  have  in  the  female  and  by  which  the  two 
sexes  can  easily  be  discriminated.  In  addition  the 
stronger  longitudinal  growth  of  the  body  in  the  male 
does  not  occur  in  the  feminized  specimens,  the  body 
growth  becomes  that  of  a  female;  and  likewise  the  fat 
and  hair  of  the  feminized  male  resemble  that  of  a  real 
female. 

While  the  castrated  males  show  an  interest  in  the 
females,  the  feminized  males  are  absolutely  indifferent 
to  females  and  behave  like  them  when  put  together 
with  normal  males ;  and,  what  is  more  interesting,  they 
are  treated  by  normal  males  like  normal  females.  The 
sexual  instincts  have,  therefore,  also  been  reversed 
in  the  feminized  males  by  the  substitution  of  ovaries 
for  testes. 


228  Basis  of  Sex  Determination 

The  inhibition  of  the  growth  of  the  penis  by  the  ovary 
is  of  importance ;  it  supports  the  idea  already  expressed 
that  in  hermaphrodites  this  inhibition  of  the  growth 
of  the  secondary  organs  of  the  other  sex  is  only  feeble 
or  does  not  exist  at  all. 

We  may  finally  ask  whether  there  is  any  connection 
between  the  cytological  basis  of  sex  determination  by 
special  sex  chromosomes  and  the  physiological  basis 
of  sex  determination  by  specific  substances  or  internal 
secretions.  It  is  possible  that  the  sex  chromosomes 
determine  or  favour,  in  a  way  as  yet  unknown,  the 
formation  of  the  specific  internal  secretion  discussed 
in  the  second  part  of  this  chapter.  In  this  way  all  the 
facts  of  sex  determination  might  be  harmonized,  and  it 
may  become  clear  that  when  it  is  possible  to  modify 
secretions  by  outside  conditions  or  to  feed  the  body 
with  certain  as  yet  unknown  specific  substances  the 
influence  of  the  sex  chromosomes  upon  the  determi- 
nation of  sex  may  be  overcome. 


CHAPTER  IX 

MENDELIAN  HEREDITY  AND  ITS  MECHANISM  ^ 
I 

I.  The  scientific  era  of  the  investigation  of  heredity 
begins  with  Mendel's  paper  on  plant  hybridization 
which  was  not  appreciated  by  his  contemporaries. 
Mendel  invented  a  method  for  the  quantitative  study 
of  heredity  which  consisted  essentially  in  crossing  two 
forms  of  peas  differing  only  in  one  well-defined  heredi- 
tary character;  and  in  following  statistically  and 
separately  the  results  of  this  crossing  and  that  of  the 
inbreeding  of  the  second  and  third  generations  of 
hybrids.  This  led  him  to  the  recognition  of  one 
essential  feature  of  heredity;  namely,  that  while  the 
hybrids  of  the  first  generation  are  all  alike,  each  hy- 
brid produces  two  types  of  sex  cells  in  equal  numbers, 
one  for  each  of  the  pure  breeds  which  has  been  used 
for  the  crossing.  This  takes  place  not  only  when  the 
forms  used  for  the  crossing  differ  in  regard  to  one 

'  For  the  literature  on  the  subject  the  reader  is  referred  to  Morgan, 
T.  H.,  Sturtevant,  A.  H.,  Muller,  H.  J.,  and  Bridges,  C.  B.,  The 
Mechanism  of  Mendelian  Heredity.     New  York,  1915. 

229 


230    Mechanism  of  Mendelian  Heredity 

character  only  but  also  if  they  differ  for  two  or  more 
characters.  The  statement  made  is  Mendel's  law  of 
heredity,  or,  more  correctly,  Mendel's  law  of  the 
segregation  of  the  hereditary  characters  of  the  parents 
in  the  sex  cells  of  the  hybrids.^  Mendel's  law  allow^s 
us  to  tabulate  and  calculate  beforehand  the  relative 
number  of  different  forms  which  appear  if  the  offspring 
of  a  mating  of  two  varieties  are  bred  among  themselves. 
In  order  to  do  this  it  must  be  remembered  also  that 
while  in  some  cases  the  hybrid  is  an  intermediate 
between  the  two  parent  forms,  in  other  cases  it  can- 
not be  discriminated  from  one  of  the  two  parent  forms. 
In  such  cases  the  character  which  appears  in  the 
hybrid  was  called  by  Mendel  the  dominant  character 
and  the  one  which  disappeared  the  recessive  character. 
According  to  Bateson,  who  was  the  first  to  systematize 
the  phenomena  of  Tvlendelian  heredity,  recessiveness 
means  generally  the  absence  of  a  character  which  is 
present  in  the  dominant  type.  When,  e.  g.,  the  cross 
between  a  tall  and  a  dwarf  form  of  pea  gives  in  the 
first  generation  only  tall  peas,  on  the  basis  of  the 
presence  and  absence  theory  the  dominant  form  con- 
tains a  factor  for  growth  which  is  lacking  in  the  dwarf 
form.  While  this  theory  fits  many  cases  it  meets  with 
difficulties  in  others.     Thus  the  presence  of  a  factor 

'  Mendel,  G.,  "Experiment  in  Plant-Hybridization,"  translated  in 
W.  Bateson's  classical  book  on  Menders  Principles  of  Heredity. 
Cambridge,  1909. 


Mechanism  of  Mendelian  Heredity    231 

for  pigment  should  be  dominant  over  the  absence  of 
such  a  factor,  which  is  usually  the  case,  inasmuch  as 
the  cross  of  a  coloured  rat  or  rabbit  with  an  albino  is 
black  or  coloured.  There  is,  however,  also  a  case  where 
whiteness  is  dominant  over  colour,  as  we  shall  see  later. 
This  fact  does  not  necessarily  contradict  the  presence 
and  absence  theory.^ 

When  two  pure  breeds  of  parents  differ  in  one  char- 
acter, e.  g.,  two  varieties  of  beans,  one  with  a  violet  the 
other  with  a  white  flow^er,  the  cross  betw^een  the  two 
species  (the  Fi  generation)  has  pale  violet  flowers, 
approximately  intermediate  between  the  two  parents. 
If  these  hybrids  are  bred  among  themselves  the  off- 
spring is  called  the  F2  generation.  According  to 
Mendel's  law  the  hybrids  of  the  first  Fj  generation  all 
have  two  kinds  of  eggs  in  equal  numbers,  one  kind 
representing  the  pure  breed  of  the  parents  with  violet, 
the  other  of  the  piire  breed  with  white  flowers.  The 
same  is  true  for  the  pollen  cells.  Hence  the  following 
possible  combinations  must  appear  in  the  offspring 
when  the  pale  violet  hybrids  are  inbred: 

violet  white eggs 


violet  white pollen 

The  four  possible  combinations  are:  (i)  violet — violet; 

» The  reader  will  find  a  critical  discussion  of  the  presence  and  absence 
theory  on  page  220  of  Morgan,  Sturtevant,  MuUer,  and  Bridges,  The 
Mechanism  of  Mendelian  Heredity.     New  York,  1915. 


2:^2    Mechanism  of  Mendelian  Heredity 

(2)  violet — white;  (3)  violet — white;  (4)  white — white. 
The  first  will  result  in  pure  violet  flowers,  the  fourth 
in  pure  white,  and  the  second  and  third  in  pale  violet 
flowers.  Since  all  four  combinations  will  appear  in 
equal  numbers  when  the  number  of  crossings  is  suffi- 
ciently large  the  numerical  result  will  be: 

violet :  pale  violet :  white  =1:2:1 

Fifty  per  cent,  of  the  F2  generation  will  be  pale 
violet,  25  per  cent,  violet,  and  25  per  cent,  white.  The 
violets  and  whites  each  will  breed  true  when  bred 
among  themselves  since  they  are  pure,  and  produce 
only  one  type  of  eggs  and  pollen.  The  pale  violets 
are  hybrids  and  will  again  produce  the  two  types 
of  eggs  and  pollen,  that  is,  if  bred  among  themselves 
will  again  give  violets,  pale  violets,  and  whites  in  the 
ratio  1:2:  I .     This  the  experiment  confirms. 

As  has  been  stated,  it  not  infrequently  happens  that 
all  the  hybrids  of  the  first  generation  are  alike.  In  such 
cases  the  one  character  is  "recessive, "  i.e.,  overshadowed 
or  covered  by  the  other  the  "dominant"  character, 
which  alone  appears  in  the  hybrids.  Thus  when 
Mendel  crossed  peas  having  round  seeds  with  peas 
having  angular  seeds  all  the  hybrids  had  round  seeds. 
The  round  form  is  dominant,  the  angular  recessive, 
i.  e.,  all  the  hybrids  have  round  seeds.  When  these 
hybrids  were  bred  among  themselves  the  next  genera- 


Mechanism  of  Mendelian  Heredity    233 

tion  produced  round  and  angular  seeds  in  the  ratio  of 
3:1  (5474  round  to  1850  angular).  The  explanation 
is  as  follows.  Let  R  denote  round,  A  angular  character ; 
the  pure  breeds  of  parents  have  the  gametic  constitu- 
tion RR  and  AA  respectively.  When  crossed,  all  the 
offsprings  have  the  constitution  RA  and  since  A  is 
recessive  this  hybrid  generation  resembles  the  pure  RR 
parents.  The  Fi  generation  produces  two  kinds  of 
eggs  R  and  A  and  two  kinds  of  pollen  R  and  A  in  equal 
numbers,  and  these  if  inbred  give  the  following  four 
combinations  in  equal  numbers: 

RR,  RA,  AR,  AA. 

Since  RA,  AR,  and  RR  all  give  round  seeds  the  Fa 
generation  produces  round  seeds  to  angular  seeds  in 
the  ratio  of  3 :  i .  The  two  organisms  with  the  gametic 
constitution  RR  and  RA  look  alike,  yet  they  are 
different  in  regard  to  heredity.  The  gametically  pure 
form  RR  is  called  homozygous,  the  impure  form  RA 
heterozygous. 

2.  W.  S.  Sutton^  was  the  first  to  show  that  the 
behaviour  of  the  chromosomes  furnishes  an  adequate 
basis  on  which  to  account  for  Mendel's  law  of  the 
segregation  of  the  characters  in  the  sex  cells  of  the 
hybrids.  If  we  disregard  the  cases  of  parthenogenesis 
and   the   X   chromosomes,    we   may   state   that   each 

^  Sutton,  W.  S.,  "The  Chromosomes  in  Heredity,"  Biol.  Bull.,  1904, 
iv.,  231. 


234    Mechanism  of  Mendelian  Heredity 

species    is   characterized    by   a    definite    number    of 
chromosomes,  e.  g.^ 

man  (probably) 24  corn 20 

mouse 20  evening  primrose 7 

snail  {Helix  hortensis) ...     22  nightshade 36 

potato  beetle 18  tobacco 24 

cotton 28  tomato 12 

four  o'clock 16  wheat 8 

garden  pea 7 

In  the  fertilization  of  the  egg  the  number  of  chro- 
mosomes is  doubled  (if  we  disregard  for  the  moment 
the  complication  caused  by  the  X  and  Y  chromosomes 
which  was  considered  in  the  previous  chapter).  It 
was  noticed  by  Montgomery  that  each  chromosome 
had  a  definite  size  and  individuality,  and  he  suggested 
that  homologous  chromosomes  existed  in  sperm  and 
egg  and  that  in  fertilization  the  homologous  chromo- 
somes of  egg  and  sperm  always  joined  and  fused  in  the 
special  stage  designated  as  synapsis,  which  will  interest 
us  later.  On  the  basis  of  this  suggestion  Sutton 
developed  the  chromosome  theory  of  the  mechanism 
of  Mendelian  heredity  or  segregation. 

According  to  this  theory,  all  the  cells  of  an  individual 
(inclusive  of  the  egg  cells  and  sperm  cells)  have  two 
sets  of  homologous  chromosomes,  one  from  the  father, 
the  other  from  the  mother.     Before  the  egg  and  sperm 

•  Morgan,  T.  H.,  Sturtevant,  A.  H.,  Muller,  H.  J.,  and  Bridges,  C. 
B.,  Mechanism  of  Mendelian  Heredity.      New  York,  1915,  p.  26. 


Mechanism  of  Mendelian  Heredity    235 

are  ready  for  the  production  of  a  new  individual,  each 
loses  one  set  of  homologous  chromosomes  in  the  so- 
called  reduction  division,  but  the  lost  set  is  made  up 
indiscriminately  of  maternal  as  well  as  paternal  chro- 
mosomes, so  that  while  one  egg  retains  the  maternal 
chromosome  A  the  other  will  retain  the  paternal  one, 
and  so  on.  If  before  the  reduction  division  all  the  eggs 
had  the  chromosome  constitution  AA^,  BB^,  CCi,  DD^ 
(where  A  B  C  D  are  the  paternal  and  A^B^  C^  Dj,  the 
maternal  chromosomes),  after  the  reduction  division 
each  daughter  cell  has  a  full  set  of  four  chromosomes, 
but  maternal  and  paternal  mixed.  Thus  the  one  cell 
may  have  ABj,CDi,  the  other  AiB^CiD,  etc.  This, 
according  to  Sutton,  is  the  basis  of  the  Mendelian 
heredity.  Suppose  the  determiner  of  a  certain  char- 
acter (violet  colour  of  flower  in  the  bean)  is  located 
in  a  chromosome  A  of  this  species.  The  homologous 
chromosome  in  beans  with  white  colour  may  be  desig- 
nated as  a.  According  to  the  chromosome  theory  of 
Mendelian  heredity  a  dijffers  from  A  in  one  point, 
though  this  difference  is  probably  only  of  a  chemical 
character  and  not  visible. 

If  an  egg  with  A  is  fertilized  by  a  pollen  with  a 
(or  vice  versa),  after  fertilization  the  chromosome  con- 
stitution of  the  fertilized  egg  is  Aa.  All  the  other 
homologous  chromosomes  are  identical  and  therefore 
need  not  be  considered.  All  the  nuclei  of  the  Fi 
generation    have    the    chromosome    constitution    Aa. 


236  Mechanism  of  Mendelian  Heredity- 
All  will  form  eggs  and  pollen  with  nuclei  of  the  same 
chromosome  constitution  Aa,  but  all  these  sex  cells 
will  go  through  the  maturation  division  before  they  are 
fertilized;  and  this  reduction  division  leads  to  the 
existence  of  two  kinds  of  eggs  in  equal  numbers,  one 
containing  only  the  A ,  the  other  only  the  a  chromosome ; 
and  the  same  happens  in  the  pollen.  When  therefore 
the  hybrids  Fi  are  mated  among  themselves,  the 
following  four  chromosome  combinations  will  be  pro- 
duced : 

Possible  combinations  in  fer- 
a,    tilized  eggs  A  A,  Aa,  aa,  in 
the  ratio  1:2:  i. 


Now  this  is  exactly  the  ratio  of  Mendelian  heredity 
in  the  F2  generation.  The  plant  with  the  chromosome 
constitution  A  A  will  form  violet  flowers,  those  with  the 
chromosome  constitution  Aa  will  form  pale  violet 
flowers,  and  those  with  the  chromosome  constitution 
aa  will  form  white  flowers. 

To  quote  Sutton's  words: 

The  result  would  be  expressed  by  the  formula  A  A:  Aa: 
aa  which  is  the  same  as  that  given  for  any  character  in  a 
Mendelian  case.  Thus  the  phenomena  of  germ  cell  divi- 
sion and  of  heredity  are  seen  to  have  the  same  essential 
features  viz.,  purity  of  units  (chromosomes,  characters) 
and  the  independent  transmission  of  the  same;  while  as  a 
corollary  it  follows  in  each  case  that  each  of  the  two  antago- 


Mechanism  of  Mendelian  Heredity    237 

nistic   units    (chromosomes,    characters)    is    contained   by 
exactly  half  the  gametes  produced. 


It  is  obvious  that  Sutton  by  this  idea  did  for  heredity 
in  general  what  McClung  had  done  for  sex  determi- 
nation or  sex  heredity,  that  is,  he  showed  that  the 
numerical  results  obtained  in  Mendelian  heredity  can 
be  accounted  for  on  the  basis  that  factors  for  hereditary 
characters  are  carried  by  definite  chromosomes.  The 
cytological  basis  of  sex  determination  becomes  only  a 
special  case  of  the  cytological  basis  of  IMendelian 
heredity.  In  the  examples  quoted  the  plants  giving 
rise  to  violet  and  to  white  flowers  are  homozygous 
for  the  colour  of  flower  having  the  chromosome  constitu- 
tion A  A  and  aa  respectively;  while  the  plants  with  pale 
violet  flowers  are  heterozygous,  having  the  chromosome 
constitution  Aa  in  their  nuclei.  The  former  give  rise 
to  identical  sex  cells  A  and  A  or  a  and  a;  while  the 
heterozygous  plants  give  rise  to  different  sex  cells  A 
and  a. 

From  this  point  of  view  in  Drosophila  (and  very 
probably  also  in  man)  the  female  is  homozygous  for 
sex  having  in  all  its  cells  the  critical  chromosome 
constitution  XX  and  giving  rise  to  one  type  of  eggs 
only,  each  with  one  X  chromosome;  while  the  male  in 
these  forms  is  heterozygous  for  sex  having  in  all  its 
cells  the  chromosome  constitution  XY  and  forming 
two  different  types  of  spermatozoa  in  equal  numbers 


238    Mechanism  of  Mendelian  Heredity 

X  and  Y.  In  Abraxas  and  in  the  fowl  the  female 
is  heterozygous  for  sex  and  the  male  homozygous. 

3.  If  the  chromosomes  are  the  vehicle  for  Mendelian 
heredity  it  should  be  possible  to  show  that  the  various 
hereditary  characters  which  follow  Mendel's  law  must 
be  distributed  over  the  various  chromosomes;  and  it 
should  be  possible  to  find  out  which  characters  are 
contained  in  the  same  chromosome.  It  has  already 
been  stated  that  sex-linked  heredity  is  intelligible  on 
the  assumption  that  the  X  chromosome  carries  the  sex- 
linked  characters.  T.  H.  JMorgan  and  his  pupils  have 
shown  with  the  greatest  degree  of  probability  that 
corresponding  linkages  occur  in  the  other  chromosomes 
and  that  there  are  in  Drosophila  exactly  as  many  groups 
of  linkage  as  there  are  different  chromosomes,  namely 
four.  ^ 

Mendel  had  found  that  when  he  crossed  two  species 
of  peas  differing  in  regard  to  two  pairs  of  characters, 
he  obtained  in  the  F2  generation  results  which  he 
calculated  on  the  assumption  that  the  segregation  of  the 
two  pairs  of  characters  in  the  sex  cells  of  the  hybrids 
took  place  independently  of  each  other.  To  illustrate 
by  an  example:  When  crossing  a  yellow  round  pea 
with  a  green  wrinkled  variety  in  which  the  characters 
round  and  yellow  are  dominant,  green  and  wrinkled 
recessive,  all  the  hybrids  of  the  F^  generation  had  the 

»  Morgan,  T.  H.,  Sturtevant,  A.  H.,  MuIIer,  H.  J.,  and  Bridges,  C.  B., 
Tlie  MecJtanism  of  Mendelian  Heredity.     New  York,  191 5. 


Mechanism  of  Mendelian  Heredity    239 

characters  round  and  yellow.  When  these  were  inbred 
the  F2  generation  produced  four  types  of  seed  in  the 
ratio  9  :  3  :  3  :  I ,  namely : 

(i)  yellow  round       (315  seeds) 

(2)  yellow  wrinkled  (loi  seeds) 

(3)  green  round         (108  seeds) 

(4)  green  wrinkled    (32  seeds) 

The  explanation  according  to  Mendel's  theory  is  as 
follows:  Since  the  segregation  of  each  pair  of  char- 
acters occurs  independently,  there  must  be  3  yellow  to  I 
green  and  also  3  round  to  i  wrinkled  in  the  F2  genera- 
tion. The  yellow  will,  therefore,  be  round  and  wrinkled 
in  the  ratio  of  3  : 1 ,  which  will  give  9  yellow  round  to  3 
yellow  wrinkled.  The  green  will  also  be  round  and 
wrinkled  in  the  ratio  of  3 :  i ,  which  will  give  3  green  round 
to  I  green  wrinkled,  which  is  the  ratio  of  9  :  3:  3:  I 
found  by  Mendel. 

On  the  basis  of  the  chromosome  theory  the  following 
explanation  could  be  given  of  this  numerical  relation. 
The  peas  with  yellow  round  seeds  have  sex  cells  with  a 
factor  for  both  yellow  and  for  round  in  two  different 
chromosomes;  these  two  different  chromosomes  we  will 
designate  with  Y  and  R.  The  peas  w^ith  green  and 
wrinkled  seeds  will  have  in  their  sex  cells  factors  for 
these  characters  in  two  homologous  chromosomes  g 
and  w,  where  g  Is  the  homologue  of  Y  and  w  of  R. 
The  cells  of  the  hybrids  of  the  F ,  generation  will  have 


240    Mechanism  of  Mendclian  Heredity 

the  chromosome  constitution  Yg  Rw,  where  Y  and  g 
and  R  and  w  are  homologous  chromosomes  which  will 
lie  alongside  each  other  g^.  In  the  formation  of  sex 
cells  a  reduction  of  these  four  chromosomes  to  two 
takes  place  whereby,  according  to  the  theory  of  Sutton, 
the  following  two  types  of  separation  can  take  place: 
YR  and  gw,  or  gR  and  Yw.  (A  separation  into  Yg 
and  Rw  is  impossible  since  the  division  takes  place 
only  between  homologous  chromosomes.)  Hence  there 
will  be  four  types  of  eggs,  YR,  gw,  gR,  and  Yw  and  the 
same  four  types  of  pollen  cells.  The  F3  generation 
will  produce  the  sixteen  possible  combinations  in  equal 
numbers:  namely, 


YRYR 

YRgw 

YRgR 

YRYw 

gw  YR 

g  w  g  w 

g  wgR 

g  w  Y  w 

gRYR 

g  R  g  w 

gRgR 

gR  Yw 

YwYR 

Y  w  g  w 

YwgR 

YwYw 

Since  w  and  g  are  recessives  and  therefore  disappear 
when  in  combination  with  their  respective  dominants 
Y  and  R  the  result  will  be  9  YR  (yellow  round),  3 
Yw  (yellow  wrinkled),  3  Rg  (round  green),  and  i  gw 
(green  wrinkled)  as  Mendel  actually  observed  and  as 
all  investigators  since  have  confirmed. 

Bateson  made  the  discovery  that  these  Mendelian 
ratios  9:3:3:  I  did  not  always  occur  when  forms 
differing  in  two  characters  were  crossed.  He  found 
typical  and  very  constant  deviations  from  this  ratio 


Mechanism  of  Mendelian  Heredity    241 

in  definite  cases  and  these  cases  he  interpreted  as  being 
due  to  "gametic  coupling." 

These  phenomena  demonstrate  the  existence  of  a  complex 
interrelation  between  the  factorial  units.  This  interrela- 
tion is  such  that  certain  combinations  between  factors  may 
be  more  frequent  than  others.  The  circumstances  in  which 
this  interrelation  is  developed  and  takes  effect  we  cannot 
as  yet  distinguish,  still  less  can  we  offer  with  confidence 
any  positive  conception  as  to  the  mode  in  which  it  is  exerted. 

Morgan  has  given  an  ingenious  explanation  of  these 
deviations  on  the  basis  of  the  chromosome  theory  of 
Mendelian  heredity.  He  assumes  that  they  occur  in 
those  cases  where  the  two  or  more  characters  are  con- 
tained in  the  same  chromosome.  In  that  case  the  two 
factors  lying  in  the  same  chromosome  should  generally 
be  found  together.  Such  was  the  case  for  instance  in 
the  experiments  with  flies  having  red  eyes  and  yellow 
body  colour  versus  white  eyes  and  grey  body  colour,  the 
character  for  white  eyes  and  yellow  body  being  located 
in  the  X  chromosome  (see  preceding  chapter),  or  in  the 
experiments  on  Abraxas.  These  phenomena  are  called 
linkage,  and  the  numerical  results  of  linkage  were  given 
in  the  preceding  chapter  in  connection  with  the  crossing 
of  sex-linked  characters. 

We  have  already  mentioned  that  before  the  matura- 
tion division  occurs  the  homologous  maternal  and 
paternal    chromosomes    fuse — the  so-called    synapsis 

» Bateson,  W.,  loc.  cit.,  p.  157. 
x6 


242     Mechanism  of  Mendelian  Heredity 

of  the  cytologists — and  afterward  separate  again.  It 
had  been  observed  by  Janssens  that  in  this  stage  of 
fusion  and  subsequent  separation  a  partial  twisting 
and  a  partial  exchange  between  two  chromosomes  may 
take  place.  Morgan  assumes  that  this  exchange 
accounts  for  certain  deviations  in  the  ratio  of  link- 


age. If  in  Fig.  40  the  white  and  black  signify  two 
homologous  chromosomes  I  and  1 1  containing  the 
two  pairs  of  homologous  factors  AB  and  ab  respectively, 
the  synapsis  state  would  be  as  in  Fig.  41.  If  the 
separation  were  complete,  either  I  or  its  homologue  Ij 
might  be  lost  in  the  maturation  division  of  the  egg. 
If,  however,  the  synapsis  is  slightly  irregular,  as  in 
Fig.  42,  where  the  chromosomes  are  slightly  twisted, 
I  and  Ix  will  not  separate  completely  but  an  exchange 


Mechanism  of  Mendelian  Heredity    243 

will  take  place,  part  of  Ii  and  I  becoming  exchanged. 
This  would  result  in  the  formation  of  two  mixed  chro- 
mosomes Ab  and  aB  (Fig.  42).  This  partial  ex- 
change of  homologous  chromosomes,  which  Morgan 
calls  "crossing  over,"  occurs,  as  he  found  in  Drosophila, 
in  the  egg  only,  not  in  the  maturation  division  of  the 
sperm.  He  informs  me  that  in  the  silkworm  moth 
Tanaka  found  that  it  occurs  only  in  the  male,  while  in 
Primula  it  takes  place  both  in  the  ovules  and  in  the 
pollen  as  shown  by  Gregory. 

Morgan  and  his  fellow-workers  have  put  this  theory 
to  nimierous  tests  by  breeding  experiments  and  the 
results  have  fully  supported  it.  According  to  the 
chromosome  theory  linkage  should  occur  only  when 
factors  lie  in  the  same  chromosome.  Hence  it  should  be 
possible,  on  the  basis  of  this  linkage  theory,  to  foretell 
how  many  linkage  groups  there  may  occur  in  a  species; 
namely,  as  many  as  there  are  chromosomes.  In 
Drosophila  there  are  four  pairs  of  chromosomes,  and 
Morgan  and  his  fellow- workers  found  only  four  groups 
of  linked  characters.  *  This  agreement  can  be  no  mere 
accident. 

Carrying  the  assumption  still  farther,  these  authors 
were  able  to  show  that  each  individual  character  has 
in  all  probability  a  definite  location  in  the  chromosome, 
so   that   it   seems   as   if  each  individual   chromosome 

'  The  number  of  hereditary  characters  examined  to  test  the  theory  was 
over  130. 


244    Mechanism  of  Mendelian  Heredity 

consisted  of  a  series  of  smaller  chromosomes,  each  of 
which  may  be  a  factor  in  the  determination  of  a  heredi- 
tary character  which  is  transmitted  according  to  Men- 
del's law  of  segregation.  Biology  has  thus  reached  in  the 
chromosome  theory  of  Mendelian  heredity  an  atomistic 
conception,  according  to  which  independent  material 
determiners  for  hereditary  characters  exist  in  a  linear 
arrangement  in  the  chromosomes. 

// 

4.  We  are  not  concerned  in  this  volume  with  the 
many  applications  of  the  theory  of  heredity  to  the 
breeding  of  plants,  animals,  and  man;  the  reader 
will  find  a  discussion  of  these  topics  in  the  numerous 
writings  of  the  special  workers  on  genetics.^  We  are, 
however,  interested  in  the  bearing  this  work  has  on 
the  conception  of  the  organism.  Two  questions  present 
themselves:  Is  the  organism  nothing  but  a  mosaic 
of  hereditary  characters  determined  essentially  by  de- 
finite elements  located  in  the  chromosomes;  and  if 
this  be  true,  what  makes  a  harmonious  whole  organism 
out  of  this  kaleidoscopic  assortment?  We  call  it  a 
kaleidoscopic  assortment  since  a  glance  at  the  Hst  of 
hereditary  characters  found  in  one  chromosome, 
according  to  Morgan,  shows  that  there  is  apparently 

»Bateson,  W.,  Mendel's  Principles  of  Heredity,  3d  ed.,  1913; 
Davenport,  Chas.  B.,  Heredity  in  Relation  to  Eugenics,  191 1.  Pearl,  R., 
Modes  of  Research  in  Genetics. 


Mechanism  of  Mendellan  Heredity    245 

no  physiological  or  chemical  connection  between 
them,  and  second :  How  can  a  factor  contained  in  the 
chromosome  determine  a  hereditary  character  of  the 
organism?  To  the  first  question  we  venture  to  offer 
the  answer  which  has  been  already  suggested  in  various 
chapters  of  this  book,  that  the  cytoplasm  of  the  egg 
is  the  future  embryo  in  the  rough ;  and  that  the  factors 
of  heredity  in  the  sperm  only  act  by  impressing  the 
details  upon  the  rough  block.  This  metaphor  will 
receive  a  more  definite  meaning  by  the  answer  to  the 
second  question.  The  characters  which  follow  Mende- 
lian  heredity  are  morphological  features  as  well  as 
instincts.  For  the  former  we  have  already  had  occa- 
sion to  show  in  previous  chapters  to  what  extent  they 
depend  upon  the  internal  secretions  or  the  existence  of 
specific  compounds  in  the  circulation,  and  the  same  is 
true  for  the  instincts  (Chapters  VIII  and  X).  This 
then  leads  us  to  the  suggestion  that  these  determiners 
contained  in  the  chromosomes  give  rise  each  to  the 
formation  of  one  or  more  specific  substances  which 
influence  various  parts  of  the  body.  We  probably 
do  not  notice  all  the  effects  in  each  case,  but  when  a 
special  organ  is  affected  in  a  conspicuous  way,  we  con- 
nect the  factor  with  this  organ  or  the  special  feature  of 
the  organ  which  is  altered,  and  speak  of  a  determiner  or 
factor  for  that  organ,  or  for  one  of  its  characters.  We 
also  understand  in  this  way  why  outside  conditions 
should  be  able  to  overcome  the  hereditary  tendency 


246    Mechanism  of  Mendelian  Heredity 

in  certain  cases,  for  instance  why  ttie  influence  of  certain 
hereditary  factors  for  pigmentation  should  depend 
upon  temperature  as  E.  Baur  observed. 

The  view,  according  to  which  the  determiners  in  the 
chromosomes  only  tend  to  give  special  characters  to 
the  embryo  or  to  the  adult  while  the  cytoplasm  of 
the  egg  may  be  considered  the  real  embryo,  receives 
some  support  from  the  fact  that  the  first  development 
of  the  egg  is  purely  maternal,  even  if  the  egg  nucleus 
has  been  replaced  by  sperm  of  a  different  species. 
If  an  egg  of  a  sea  urchin  be  cut  into  two  pieces,  one 
with  and  one  without  a  nucleus,  and  the  enucleated 
piece  be  fertilized  with  the  sperm  of  a  different  species  of 
sea  urchin,  the  blastula  and  gastrula  stages  are  purely 
maternal  and  only  the  skeleton  of  the  pluteus  stage 
begins  to  betray  the  influence  of  the  foreign  sperm 
inasmuch  as  this  skeleton  is  purely  paternal,  according 
to  Boveri.  In  all  experiments  on  hybridization  it  has 
been  found  that  the  rate  of  cell  division  of  the  egg  is  a 
purely  maternal  character.  Thus  when  fish  eggs  of  a 
species,  in  which  the  rate  of  first  segmentation  of  the 
egg  is  about  eight  hours,  are  fertilized  with  sperm  of  a 
species  for  which  the  same  process  requires  about 
thirty  minutes  or  less  at  the  same  temperature,  the 
rate  of  segmentation  is  again  about  eight  hours.  There 
is  then  no  chromosome  Influence  noticeable  In  the  early 
development. 

When  two  forms  of  sea  urchins,  Strongylocentrotus 


Mechanism  of  Mendelian  Heredity    247 

franciscanus  and  purpuratus/  are  crossed,  certain 
features  of  the  skeleton  of  the  embryo,  e.  g. ,  the  so-called 
cross-bars,  are  a  dominant,  inasmuch  as  they  are  found 
in  purpuratus  and  both  the  crosses,  while  they  are 
absent  in  franciscanus.  The  development  prior  to 
the  formation  of  the  skeleton  is  purely  maternal. 
These  observations  again  lend  support  to  the  idea  that 
the  Mendelian  factors  of  heredity  must  have  the 
embryo  to  work  on  and  that  the  organism  is  not  to  be 
considered  a  mere  mosaic  of  Mendelian  factors.  This  is 
further  supported  by  the  idea  that  the  species  specificity 
resides  in  the  proteins  of  the  unfertilized  egg  (see  Chap- 
ter III),  and  it  is  quite  likely  that  this  species  specificity 
decides  which  type  of  animal  should  arise  from  an  egg. 
The  idea  had  been  suggested  that  the  factors  which 
determine  the  future  character  might  be  ferments  or 
enzymes,  or  substances  from  which  such  ferments  de- 
velop. A.  R.  Moore  ^  pointed  out  that  the  cross-bars  in 
the  skeleton  of  the  hybrid  between  S.  purpuratus  and 
franciscanus  develop  more  slowly  than  in  the  pure  breed 
and  that  this  should  be  expected  if  the  determiners  were 
enzymes.  Since  the  pure  purpuratus  has  two  deter- 
miners for  the  development  of  the  cross-bars  (from 
both  egg  and  sperm) ,  the  hybrids  only  one  (from  either 

'  Loeb,  J., King,  W.  O.  R.,  and  Moore,  A.  R.,  Arch.f.  Entwcklngsmech., 
19 10,  xxix.,  354.  These  experiments  have  been  repeated  at  different 
seasons  of  the  year  and  in  different  years  and  have  been  found  to  be 
constant. 

^  Moore,  A.  R.,  Arch.f.  Entwcklngsmech.,  1912,  xxxiv.,  168. 


248    Mechanism  of  Mendelian  Heredity 

egg  or  sperm),  the  pure  purpuratus  should  have  twice 
the  enzyme  mass  of  the  hybrid.  It  is  known  that  the 
velocity  of  a  chemical  reaction  increases  in  proportion 
with  the  mass  (or  in  some  cases  in  proportion  with 
the  square  root  of  the  mass)  of  the  enzyme;  the  cross- 
bars should  therefore  develop  faster  in  the  pure  than 
in  the  hybrid  breeds,  as  was  observed  by  Moore.  It 
was,  however,  not  possible  to  obtain  quantitative  data. 

On  the  other  hand,  it  is  obvious  that  this  reasoning 
would  not  hold  for  all  cases.  Thus  when  beans  with 
violet  flowers  are  crossed  with  white-flowered  beans 
the  hybrids  are  pale  blue,  which  indicates  that  the 
hybrids  have  less  pigment  than  the  pure  violet.  Now 
we  know  that  the  mass  of  enzyme  does  not  influence 
the  chemical  equilibrium  but  only  the  velocity  of  the 
reaction.  The  hybrids  and  pure  violets  differ,  how- 
ever, in  the  mass  of  violet  pigment  formed,  that  is  to 
say,  in  regard  to  the  equilibrium.  Hence  the  idea  that 
the  determiners  are  enzymes  or  give  rise  to  enzymes  is 
probably  not  applicable  to  cases  of  this  type. 

The  experiments  on  the  heredity  of  pigments  are 
at  present  almost  the  only  ones  which  can  be  used  for 
an  analysis  of  the  chemical  nature  of  the  character 
and  its  possible  determiner.  The  important  work  of 
G.  Bertrand'  and  of  Chodat^  on  the  production  of 

^Bertrand,  G.,  Ann.  d.  I' Inst.  Pasteur,  1908,  xxii.,  381;  Bull.  Soc. 
Chim.,  1896,  XV.,  791. 

'  Chodat,  R.,  Arch.  d.  Sc.  phys.  et  nat.,  1915,  xxxix.,  327. 


Mechanism  of  Mendelian  Heredity    249 

black  pigment  in  the  cells  of  animals  and  plants  with 
the  aid  of  enzymes  has  paved  the  way  for  such  work. 
Bertrand  has  shown  that  tyrosine  (^-oxyphenylamino- 
propionic  acid)  is  transformed  into  a  black  pigment 
by  an  enzyme  tyrosinase  which  occurs  in  numerous 
organisms  and  is  obviously  the  cause  of  pigment  and 
colouration  in  a  great  number  of  species.  This  discovery 
was  utilized  in  the  study  of  the  heredity  of  pigments 
by  Miss  Durham,  Gortner,^  and  very  recently  by  On- 
slow.^ The  latter  showed  that  from  the  skins  of  cer- 
tain coloured  rabbits  and  mice  a  peroxidase  can  be 
extracted  which  behaves  like  a  tryosinase  toward 
tyrosine  in  the  presence  of  hydrogen  peroxide.  This 
peroxidase  was  found  in  the  skins  of  black  agouti, 
chocolate  and  blue  rabbits,  but  not  in  yellow  or  orange 
rabbits.  The  recessive  whiteness  in  rabbits  and  mice 
according  to  this  author  is  due  to  the  lack  of  the  per- 
oxydase.  There  exists  a  dominant  whiteness  in  the 
English  rabbit  which  is  due  to  a  tyrosinase  inhibitor 
which  destroys  the  activity  of  the  tyrosinase  "and  the 
dominant  white  bellies  of  yellow  and  agouti  rabbits 
are  due  to  the  same  cause."  "Variations  in  coat  colour 
are  probably  due  to  a  quantitative  rather  than  to  a 
qualitative  difference  in  the  pigment  present." 

One  point  might  still  be  mentioned  since  it  may  help 
to  overcome  a  difficulty  in  visualizing  the  connection 

'  Gortner,  R.  A.,  Trans.  Chem.  Soc,  1910,  xcvii.,  no. 
'Onslow,  H.,  Proc.  Roy.  Soc,  1915,  B.  Ixxxix.,  36. 


250    jMechanism  of  Mendelian  Heredity 

between  the  localization  of  a  factor  in  the  chromosome 
and  the  production  of  a  comparatively  large  quantity  of 
a  specific  chemical  compound,  e.  g.,  a  chromogen  or  a 
tyrosinase.  We  must  remember  that  all  the  cells  of 
an  organism  have  identical  chromosomes,  so  that 
a  factor  for  an  enzyme  like  tyrosinase  is  contained 
in  every  cell  throughout  the  whole  body.  It  is 
likely,  however,  that  the  same  factor  (which  we  may 
conceive  to  be  a  definite  chemical  compound)  will 
find  a  different  chemical  substrate  to  work  on  in 
the  cells  of  different  organs  of  the  body,  since  the 
different  organs  differ  in  their  chemical  composition. 
Thus  it  is  conceivable  that  in  the  production  of  tyro- 
sinase or  of  tyrosine  not  a  single  chromomere  of  one 
single  cell  is  engaged,  but  the  sum  total  of  all  these 
individual  chromomeres  of  all  the  cells  in  one  or  several 
organs  of  the  body.  The  writer  has  added  this  remark 
especially  in  consideration  of  the  fact  that  some  authors 
seem  to  feel  that  the  chromosome  conception  of  heredity 
is  incompatible  with  a  physicochemical  view  of  this 
process. 

Since  we  have  mentioned  this  difficulty  which  some 
writers  seem  to  find  in  the  chromosome  theory  of  Men- 
delian heredity,  it  may  be  added  that  a  single  factor 
may  suffice  to  determine  a  series  of  complicated  reflexes. 
Thus  the  heliotropic  reactions  of  animals  are  due  to  the 
presence  of  photosensitive  substances,  and  it  suffices 
for   the   hereditar}^   transmission   of    the   complicated 


Mechanism  of  Mendelian  Heredity    251 

purposeful  reactions  based  on  these  tropisms  that  a 
factor  for  the  formation  of  the  photosensitive  substance 
should  exist.  ^ 

5,  Another  point  should  be  emphasized,  namely 
that  for  Mendelian  heredity  it  is  immaterial  whether 
the  character  is  introduced  by  the  spermatozoon  or 
by  the  egg.  This  fact  which  Mendel  himself  already 
recognized  is  in  full  harmony  with  the  conclusion  that 
the  chromosomes  and  not  the  cytoplasm  are  the  bearers 
of  Mendelian  heredity,  since  only  in  respect  to  the 
chromosome  constitution  are  egg  and  sperm  alike, 
while  they  differ  enormously  in  regard  to  the  mass  of 
protoplasm  they  carry.  We  can,  therefore,  be  tolerably 
sure  that  wherever  we  deal  with  a  hereditary  factor 
which  is  determined  by  the  egg  alone  the  cytoplasm 
of  the  latter  is  partly  or  exclusively  responsible  for  the 
result. 

We  have  already  mentioned  the  fact  that  the  rate  of 
segmentation  of  the  egg  is  such  a  character.  Yet 
this  character  is  as  definite  as  any  Mendelian  character, 
and  it  would  be  as  easy  to  discriminate  two  species 
of  eggs  by  the  time  required  from  insemination  to  the 
beginning  of  cell  division  as  it  would  be  by  any  Men- 
delian character  of  their  parents. 

The  application  of  our  modern  knowledge  of  heredity 
to  human  affairs  has  been  discussed  in  a  very  original 

'  Loeb,  J.,  "Egg  Structure  and  the  Heredity  of  Instincts,"  The  Monist, 
1897,  vii.,  481. 


252    Mechanism  of  Mendelian  Heredity 

way  by  Bateson  in  his  address  before  the  British 
Association  in  Sydney  to  which  the  reader  may  be 
referred.  ^ 

'  Bateson,  W.,  Nature,  1916,  xciii,,  674. 


CHAPTER  X 

ANBIAL    IX5TI^XTS    AND    TROPISMS^ 

I.  The  idea  that  the  organism  as  a  whole  cannot 
be  explained  from  a  physicochemical  viewpoint  rests 
most  strongly  on  the  existence  of  animal  instincts 
and  will.  Many  of  the  instinctive  actions  are  "pur- 
poseful," i.  e.,  assisting  to  preserve  the  individual  and 
the  race.  This  again  suggests  "design"  and  a  design- 
ing "force,"  w^hich  we  do  not  find  in  the  realm  of 
physics.  We  must  remember,  however,  that  there  vras 
a  time  when  the  same  "purposefulness"  was  believed 
to  exist  in  the  cosmos  where  everything  seemed  to 
turn  literally  and  metaphorically  around  the  earth, 
the  abode  of  man.  In  the  latter  case,  the  anthropo- 
or  geocentric  view  came  to  an  end  when  it  was  shown 
that  the  motions  of  the  planets  were  regulated  by 
Newton's  law  and  that  there  was  no  room  left  for  the 

*  Ideas  similar  to  those  expressed  in  tliis  chapter  may  be  found  in  the 
writer's  former  book  Comparative  Physiology  of  tlie  Brain  and  Compara- 
tive Psychology,  New  York,  1900,  and  in  the  books  by  George  Bohn, 
La  Naissance  de  l' Intelligence,  Paris,  1909,  and  La  nouvelle  Psychologie 
animale,  Paris,  191 1. 

253 


254       Animal  Instincts  and  Tropisms 

activities  of  a  guiding  power.  Likewise,  in  the  realm 
of  instincts  when  it  can  be  shown  that  these  instincts 
may  be  reduced  to  elementary  physicochemical  laws 
the  assumption  of  design  becomes  superfluous. 

If  we  look  at  the  animal  instincts  purely  as  observers 
we  might  well  get  the  impression  that  they  cannot  be 
explained  in  mechanistic  terms.  We  need  only  consider 
what  mysticism  apparently  surrounds  all  those  instincts 
by  which  the  two  sexes  are  brought  together  and  by 
which  the  entrance  of  the  spermatozoon  into  the  egg 
is  secured;  or  the  remarkable  instincts  which  result  in 
providing  food  and  shelter  for  the  young  generation. 

We  have  already  had  occasion  to  record  some  cases 
of  instincts  which  suggest  the  possibility  of  physico- 
chemical  explanation;  for  example  the  curious  experi- 
ment of  Steinach  on  the  reversal  of  the  sexual  instincts 
of  the  male  whose  testes  had  been  exchanged  for 
ovaries.  There  is  little  doubt  that  in  this  case  the 
sexual  activities  of  each  sex  are  determined  by  specific 
substances  formed  in  the  interstitial  tissue  of  the 
ovary  and  testes.  The  chemical  isolation  of  the 
active  substances  and  an  investigation  of  their  action 
upon  the  various  parts  of  the  body  would  seem  to 
promise  further  progress  along  this  line. 

Marchal's  observations  on  the  laying  of  eggs  by  the 
naturally  sterile  worker  wasps  are  a  similar  case.  The 
fact  that  such  workers  lay  eggs  when  the  queen  is 
removed  or  when  they  are  taken  away  from  the  larvag 


Animal  Instincts  and  Tropisms       255 

may  be  considered  as  a  manifestation  of  one  of  those 
wonderful  instincts  which  form  the  dehght  of  readers 
of  Maeterlinck's  romances  from  insect  life.  Imagine 
the  social  foresight  of  the  sterile  workers  who  when  the 
occasion  demands  it  "raise"  eggs  to  preserve  the  stock 
from  extinction !  And  yet  what  really  happens  is  that 
these  workers,  when  there  are  no  larvae,  can  consume 
the  food  which  would  otherwise  have  been  devoured 
by  the  larvse;  and  some  substance  contained  in  this 
food  induces  the  development  of  eggs  in  the  otherwise 
dormant  ovaries.  What  appeared  at  first  sight  as  a 
mysterious  social  instinct  is  revealed  as  an  effect 
comparable  to  that  of  thyroid  substance  upon  the 
growth  of  the  legs  of  tadpoles  in  Gudernatsch's 
experiment  (Chapter  VII). 

2.  If  we  wish  to  show  in  an  unmistakable  way  the 
mechanistic  character  of  instincts  we  must  be  able  to 
reduce  them  to  laws  which  are  also  valid  in  physics. 
That  instinct,  or  rather  that  group  of  instincts,  for 
which  this  has  been  accomplished  are  the  reactions 
of  organisms  to  light.  The  reader  is  familiar  with  the 
tendency  of  many  insects  to  fly  into  the  flame.  It 
can  be  shown  that  many  species  of  animals,  from  the 
lowest  forms  up  to  the  fishes,  are  at  certain  stages — 
very  often  the  larval  stage — of  their  existence,  slaves  of 
the  light.  When  such  animals,  e.  g.,  the  larv^  of  the 
barnacle  or  certain  winged  plant  lice  or  the  cater- 
pillars of  certain  butterflies,  are  put  into  a  trough  or 


256       Animal  Instincts  and  Tropisms 

test-tube  illuminated  from  one  side  only,  they  will  rush 
to  the  side  from  which  the  light  comes  and  will  continue 
to  do  this  whenever  the  orientation  of  the  trough 
or  test-tube  to  the  light  is  changed;  while  they  will  be 
held  at  the  window  side  of  the  vessel  if  the  light  or 
the  position  of  the  vessel  remains  unchanged.  This 
instinct  to  get  to  the  source  of  light  is  so  strong  that, 
e.  g.,  the  caterpillars  of  Porthesia  chrysorrJicea  die  of 
starvation  on  the  window  side  of  the  vessel,  with  plenty 
of  food  close  behind.  This  powerful  "instinct"  is, 
as  we  intend  to  show,  in  the  last  analysis,  the  expres- 
sion of  the  Bunsen-Roscoe  law  of  photochemical  re- 
actions. A  large  number  of  chemical  reactions  are 
induced  or  accelerated  by  light,  and  the  Bunsen-Roscoe 
law  shows  that  the  chemical  effect  is  in  these  cases, 
within  certain  limits,  equal  to  the  product  of  the  in- 
tensity into  the  duration  of  illumination. 

The  "attraction"  or  "repulsion"  of  animals  by  the 
light  had  been  explained  by  the  biologists  in  an  anthro- 
pomorphic way  by  ascribing  to  the  animals  a  "fond- 
ness" for  light  or  for  darkness.  Thus  Graber,  who  had 
made  the  most  extensive  experiments,  gave  as  a  result 
the  statement  that  animals  which  are  fond  of  light 
are  also  fond  of  blue  while  they  hate  the  red,  and 
those  which  are  fond  of  the  "dark"  are  fond  of  red  and 
hate  the  blue.^     In  1888  the  writer  published  a  paper 

'  Graber,  V.,  Grundlinien  zur  Erforschung  des  HelUgkeils-  und 
Farbensinnes  der  Tiere.     Prag,  1884. 


Animal  Instincts  and  Troplsms       257 

in  which  he  pointed  out  that  the  so-called  fondness  of 
animals  for  light  and  blue  and  for  dark  and  red  was 
simply  a  case  of  an  automatic  orientation  of  animals 
by  the  light  comparable  to  the  turning  of  the  tips  of  a 
plant  towards  the  window  of  the  room  in  which  the 
plant  is  raised.^ 

The  phenomenon  of  a  plant  bending  or  growing  to  the 
source  of  light  is  called  positive  heliotropism  (while 
we  speak  of  negative  heliotropism  in  all  cases  in  which 
the  plant  turns  away  from  the  light,  as  is  observed 
in  many  roots).  The  writer  pointed  out  that  animals 
which  go  to  the  light  are  positively  heliotropic  (or 
phototropic)  and  do  so  because  they  are  compelled 
automatically  by  the  light  to  move  in  this  direction, 
while  he  called  those  animals  which  move  away  from 
the  light  negatively  hehotropic ;  they  are  automatically 
compelled  by  the  light  to  move  away  from  it.  What 
the  light  does  is  to  direct  the  motions  of  the  animals 
and  to  explain  this  the  following  theory  was  proposed. 
Animals  possess  photosensitive  elements  on  the  surface 
of  their  bodies,  in  the  eyes,  or  occasionally  also  in 
epithelial  cells  of  their  skin.  These  photosensitive 
elements  are  arranged  symmetrically  in  the  body  and 
through  nerves  are  connected  with  symmetrical  groups 
of  muscles.     The  light  causes  chemical  changes  in  the 

'  Loeb,  J.,  Sitzungsber.  d.  physik.-med.  Gesellsch.      Wurzburg,  1888. 
Der  TIeliotropismus  der  Tiere  und  seine  Ubereinstimmung  mit  dent  Helio- 
tropismus  der  Pflanzen.    Wurzburg,  1889.    Arch.  f.  d.  ges.  Physiol., 
1897,  Ixvi.,  439. 
17 


258       Animal  Instincts  and  Tropisms 

eyes  (or  the  photosensitive  elements  of  the  skin).  The 
mass  of  photochemical  reaction  products  formed  in 
the  retina  (or  its  homologues)  influences  the  central 
nervous  system  and  through  this  the  tension  or  energy 
production  of  the  muscles.  If  the  rate  of  photo- 
chemical reaction  is  equal  in  both  eyes  this  effect 
on  the  symmetrical  muscles  is  equal,  and  the  muscles 
of  both  sides  of  the  body  work  with  equal  energy;  as  a 
consequence  the  animal  will  not  be  deviated  from  the 
direction  in  which  it  was  moving.  This  happens  when 
the  axis  or  plane  of  symmetry  of  the  animal  goes  through 
the  source  of  light,  provided  only  one  source  of  light 
be  present.  If,  however,  the  light  falls  sidewise  upon 
the  animal,  the  rate  of  photochemical  reaction  will  be 
unequal  in  both  eyes  and  the  rate  at  which  the  sym- 
metrical muscles  of  both  sides  of  the  body  work  will 
no  longer  be  equal;  as  a  consequence  the  direction 
in  which  the  animal  moves  will  change.  This  change 
will  take  place  in  one  of  two  ways,  according  as  the 
animal  is  either  positively  or  negatively  heliotropic;  in 
the  positively  heHotropic  animal  the  resulting  motion 
will  be  toward,  in  the  negatively  heliotropic  from,  the 
light.  Where  we  have  no  central  nervous  system,  as 
in  plants  or  lower  animals,  the  tension  of  the  contractile 
or  turgid  organs  is  influenced  in  a  different  way,  which 
we  need  not  discuss  here. 

The    reader    will    perceive    that    according    to    the 
writer's  theory  two  agencies  are  to  be  considered  in 


Animal  Instincts  and  Tropisms       259 

these  reactions:  first,  the  symmetrical  arrangement  of 
the  photosensitive  and  the  contractile  organs,  and  sec- 
ond, the  relative  masses  of  the  photochemical  reaction 
products  produced  in  both  retinae  or  photosensitive 
organs  at  the  same  time.  If  a  positively  heliotropic 
animal  is  struck  by  light  from  one  side,  the  effect  on 
tension  or  energy  production  of  muscles  connected 
with  this  eye  will  be  such  that  an  automatic  turning 
of  the  head  and  the  whole  animal  towards  the  source  of 
light  takes  place ;  as  soon  as  both  eyes  are  illuminated 
equally  the  photochemical  reaction  velocity  will  be 
the  same  in  both  eyes,  the  symmetrical  muscles  of  the 
body  will  work  equally,  and  the  animal  will  continue 
to  move  in  this  direction.  In  the  case  of  the  nega- 
tively heliotropic  animal  the  picture  is  the  same  except 
that  if  only  one  eye  is  illuminated  the  muscles  connected 
with  this  eye  will  work  less  energetically.  The  theory 
can  be  nicely  tested  for  negatively  heliotropic  animals 
in  the  larv^  of  the  blowfly  when  they  are  fully  grown, 
and  for  positively  heliotropic  animals  on  the  larvce  of 
Balanus,  and  many  other  organisms. 

One  of  the  difficulties  in  identifying  the  motions 
of  animals  to  or  from  the  light  with  the  positive  and 
negative  heliotropism  of  plants  consisted  in  the  fact 
that  plants  are  mostly  sessile  (and  respond  to  a  one- 
sided illumination  with  heliotropic  curvatures  to  or 
from  the  light),  while  most  animals  are  free  moving 
and  respond  to  the  one-sided   illumination  by  being 


26o       Animal  Instincts  and  Tropisms 

turned  and  compelled  to  move  to  or  from  the  light. 
This  difficulty  was  overcome  by  the  observation  that 


Fig.  43 

sessile  animals  like  the  hydroid  Eudendrium  (Fig.  43) 
or  the  tube  worm  Spirographis  (Fig.  44)  react  to  a  one- 


FlG.  44 

sided  illumination  also  with  heliotropic  curvatures  like 

sessile  plants.^     On  the  other  hand,  it  had  been  found 

before    by     Strassburger    that     free-swimming     plant 

*  Loeb,  J.,  Arch.j.  d.  ges.  Physiol.,  1890,  xlvii.,  391;  1896,  Ixiii.,  273. 


Animal  Instincts  and  Tropisms       261 

organisms  like  the  swarmspores  of   algae  move  to  or 
from  the  source  of  light  as  do  free-swimming  animals. 

3.  The  writer  suggested  in  1897^  that  the  light  acts 
chemically  in  the  heliotropic  reactions  and  in  1912  that 
the  heliotropic  reactions  probably  follow  the  law  of 
Bunsen  and  Roscoe,^  and  it  was  possible  to  confirm 
this  idea  by  direct  experiments.  ^  This  law  states 
that  the  photochemical  effect  of  light  equals  i  t  where  i 
is  the  intensity  of  the  light  and  t  the  duration  of  illumi- 
nation. The  experiments  were  carried  out  on  young 
regenerating  polyps  of  Eudendrium  by  measuring  the 
time  required  to  cause  fifty  per  cent,  of  the  polyps 
to  bend  to  the  source  of  light.  The  intensity  of  light 
was  varied  by  altering  the  distance  of  the  source  of 
light  from  the  polyps.     Table  VI  gives  the  result. 

TABLE  VI 


Distance  between  Polyps 

Time  Required  to  Cause  Fifty  Per  Cent,  of  the 
Polyps  to  Bend  towards  the  Source  of  Light 

and  Source  of  Light 

Observed 

Calculated  from 
bunsen-roscoe  law 

Metres 

0.25 
0.50 
1. 00 
1.50 

Minutes 

10 

between  35  and  40 

150 
between  360  and  420 

Minutes 

40 
160 

360 

^  Loeb,  J.,  Arch.  f.  d.  ges.  Physiol.,  1897,  Ixvi.,  439. 

» Loeb,  J.,  The  Mechanistic  Coiiception  of  Life,  Chicago,  1912,  p.  27, 

3  Loeb,  J.,  and  Ewald,  W.  F.,  Zentralbl.f.  Physiol.,  1914,  xxvii.,  1165. 


262       Animal  Instincts  and  Tropisms 

We  must  therefore  conclude  that  the  heliotropic 
curvature  of  the  polyps  is  determined  by  a  photochemi- 
cal action  of  the  light.  The  light  brings  about  or 
accelerates  a  chemical  reaction  which  follows  the  Bunsen- 
Roscoe  law.  As  soon  as  the  product  of  this  reaction 
on  one  side  of  the  polyp  exceeds  that  on  the  other  by 
a  certain  quantity,  the  bending  occurs.  When  the 
product  it  is  the  same  for  symmetrical  spots  of  the 
organism  no  bending  can  result.  This  is  what  our 
theory  suggested. 

It  is  very  difficult  to  prove  directly  the  applicability 
of  the  Bunsen-Roscoe  law  for  free-moving  animals, 
but  it  can  be  shown  that  intermittent  light  is  as  effect- 
ive as  constant  light  of  the  same  intensity,  provided 
that  the  total  duration  of  the  illumination  by  the 
intermittent  light  is  equal  to  that  of  the  constant  light, 
and  the  duration  of  the  intermission  is  sufficiently  small 
(Talbot's  law).  Talbot's  law  is  in  reality  only  a  modi- 
fication of  the  Bunsen-Roscoe  law.  Ewald  has  proved 
in  a  very  elegant  way  the  applicability  of  Talbot's 
law  to  the  orientation  of  the  eyestalk  of  Daphnia.'^ 
This  makes  it  probable  that  the  law  of  Bunsen-Roscoe 
underlies  generally  the  heliotropic  reaction  of  animals. 

It  is  of  importance  for  the  theory  of  the  identity 
of  the  heliotropisni  of  animals  and  plants  that  in  the 
latter  organisms  the  law  of  Bunsen  and  Roscoe  is  also 
applicable.     This    had    been    shown    previously    by 

'  Ewald,  W.  F.,  Science,  1913,  xxxviii.,  236. 


Animal  Instincts  and  Tropisms       263 

Froschel^  and  by  Blaauw.''  In  the  following  table 
are  given  the  results  of  Blaauw's  experiments  on  the 
applicability  of  the  Bunsen-Roscoe  law  for  the  heHo- 
tropic  curvature  of  the  seedHngs  of  oats  (Avena  saliva). 
The  time  required  to  cause  heHotropic  curvatures  for 
intensities  of  light  varying  from  0.00017  to  26520 
mxCtre-candles  was  measured.  The  product  it,  namely 
metre-candles-seconds,  varies  very  little  (between  16 
and  26). 

TABLE  VII 


I 

II 

III 

I 

II: 

III 

Duratio7i  of 

Metre- 

Metre- 

Dtiration  of 

Metre- 

Metre- 

Illumination 

Candles 

Candles- 
Seconds 

Illumination 

Candles 

Candles- 
Seconds 

43  hours 

0.00017 

26.3 

25  seconds 

1.0998 

27-5 

13 

0.000439 

20.6 

8 

3.02813 

24.2 

10 

0.000609 

21.9 

4 

5456 

21.8 

6 

0.000855 

18.6 

2 

8.453 

16.9 

3     .    " 

0.001769 

19.1 

I         " 

18.94 

18.9 

100  minutes 

0.002706 

16.2 

2/5         " 

45-05 

18.0 

60 

0.004773 

17.2 

2/25         " 

308.7 

24.7 

3°    :; 

0.01018 

18.3 

1/25         " 

5114 

20.5 

20 

0.01640 

19.7 

^55     ;; 

1255 

22.8 

15 

0.0249 

22.4 

i/ioo 

1902 

19.0 

8 

0.0498 

23-9 

1/400 

7905 

19.8 

4        " 

0.0898 

21.6 

1/800       " 

13094 

16.4 

40  seconds 

0.6156 

24.8 

i/iooo         " 

26520 

26.5 

It  is,  therefore,  obvious  that  the  bHnd  instinct 
which  forces  animals  to  go  to  the  light,  e.  g.,m  the  case 
of  the  moth,  is  identical  v^ith  the  instinct  which  makes 

^  Froschel,  P.,  Sitzungsher.  d.  k.Akad.  d.  Wissensch. ,V7ien,  I908,cxvii. 
'  Blaauw,  H.  A.,  Rec.  d.  travaux  botanigites  Neerlandais,  1909,  v.,  209. 


264       Animal  Instincts  and  Tropisms 

a  plant  bend  to  the  light  and  is  a  special  case  of  the 
same  law  of  Bunsen  and  Roscoe  which  also  explains 
the  photochemical  effects  in  inanimate  nature;  or  in 
other  words,  the  will  or  tendency  of  an  animal  to  move 
towards  the  hght  can  be  expressed  in  terms  of  the 
Bunsen-Roscoe  law  of  photochemical  reactions. 

The  writer  had  shown  in  his  early  publications  on 
light  effects  that  aside  from  the  heliotropic  reaction  of 
animals,  which  as  we  now  know  depends  upon  the 
product  of  the  intensity  and  duration  of  illumination, 
there  is  a  second  reaction  which  depends  upon  the 
sudden  changes  in  the  intensity  of  illumination.  These 
latter  therefore  obey  a  law  of  the  form:  Effect  =  f  (^).^ 
Jennings  has  maintained  that  the  heliotropic  reactions 
of  unicellular  organisms  are  all  of  this  kind,  but  in- 
vestigations by  Torrey  and  by  Bancroft^  on  Euglena 
have  shown  that  Jennings's  statements  were  based  on 
incomplete  observations. 

4,  In  these  experiments  only  one  source  of  light  was 
applied.  "When  two  sources  of  light  of  equal  intensity 
and  distance  act  simultaneously  upon  a  heliotropic 
animal,  the  latter  puts  its  median  plane  at  right  angles 
to  the  line  connecting  the  two  sources  of  light.  "^ 
This  fact  has  been  amply  verified  by  Bohn,  by  Parker 
and  his  pupils,  and  especially  by  Bradley  Patten,  who 

'  Loeb,  J.,  Arch.  f.  d.  ges.  Physiol.,  1893,  liv.,  81;  Jour.  Exper.  Zool.f 
1907,  iv.,  151. 

'Bancroft,  F.  W.,  Jour.  Exper.  Zool.,  1913,  xv.,  383. 

3  Loeb,  J.,  Studies  in  General  Physiology,  Chicago,  1905,  p.  2. 


Animal  Instincts  and  Tropisms       265 

used  it  to  compare  the  relative  efficiency  of  two  different 
lights. 

The  behaviour  of  the  animals  under  the  influence  of 
two  lights  is  a  confirmation  of  our  theory  of  heliotro- 
pism  inasmuch  as  the  animal  moves  in  such  a  direction 
that  the  symmetrical  elements  of  the  surface  of  the 
body  are  struck  by  light  of  the  same  intensity  at  the 
same  angle,  so  that  as  a  consequence  equal  masses  of 
photosensitive  substances  are  produced  in  symmetrical 
elements  of  their  eyes  or  skin  in  equal  times.  The 
effect  on  the  symmetrical  muscles  will  be  identical. 
As  soon  as  one  of  the  lights  is  a  little  stronger  the 
animal  will  deviate  towards  this  light,  in  case  it  is 
positively  heliotropic  and  towards  the  weaker  light  if  it 
is  negatively  heliotropic.  This  deviation  again  is  not 
the  product  of  chance  but  follows  a  definite  law  as 
Patten*  has  recently  shown.  He  used  the  negatively 
heliotropic  larvae  of  the  blowfly.  These  larvas  were 
made  to  record  their  trail  while  moving  under  the 
influence  of  the  two  lights.  The  results  of  the  measure- 
ments of  2500  trails  showing  the  progressive  increase 
in  angular  deviation  of  the  larva  (from  the  perpendicular 
upon  the  line  connecting  the  two  hghts) ,  with  increasing 
differences  between  the  lights,  are  given  in  the  follow- 
ing table.  Since  the  deviation  or  angular  deflection  of 
the  larvae  is  towards  the  weaker  of  the  two  lights  it  is 
marked  negative. 

'  Patten,  Bradley  M.,  Am.  Jour.  Physiol.,  1915,  xxxviii.,  313. 


266       Animal  Instincts  and  Tropisms 

TABLE  VIII 


Percentage  Difference  in  the 

Av 

erage  Angular  Deflection 

of  the 

Intensity  of  the  Tu 

'0  Lights 

Ti 

I'o  Paths  of  the  Larvce  toi. 
the  Weaker  Light 

vards 

Per  Cent. 

Degrees 

0 

—  0.09^ 

m 

-  2.77 

16M 

-  5-75 

25 

-  8.86 

33M 

—  11.92 

50 

—20.28 

66% 

-30.90 

83M 

-46.81 

100 

-77-56 

Let  us  assume  that  the  negatively  heliotropic  animal 
is  at  an  equal  distance  from  the  two  unequal  lights  and 
placed  so  that  at  the  beginning  of  the  experiment  its 
median  plane  is  at  right  angles  to  the  line  connecting 
the  two  lights,  but  with  its  head  turned  away  from 
them.  In  that  case  the  velocity  of  reaction  in  the 
symmetrical  photosensitive  elements  of  the  eyeless 
larvae  is  greater  on  the  side  of  the  stronger  light.  Since 
the  animal  is  negatively  heliotropic  this  will  result  in  a 
greater  relaxation  or  a  diminution  of  the  energy  pro- 
duction of  the  muscles  turning  the  head  of  the  animal 
towards  the  side  of  the  stronger  light.  Hence  the 
animal  will  automatically  deviate  from  the  straight 
line  towards  the  side  of  the  weaker  light.  By  the 
alteration  of  the  position  of  its  body  the  photosensitive 
elements  exposed   to  the   stronger  of  the  two  lights 


Animal  Instincts  and  Tropisms        267 

will  be  put  at  a  less  efficient  angle  and  hence  the  rate 
of  photochemical  reaction  on  this  side  will  be  diminished. 
The  deviation  from  the  perpendicular  in  which  the 
animal  will  ultimately  move  will  be  such  that  as  a 
consequence,  the  rate  of  photochemical  reaction  in 
symmetrical  elements  is  again  equal.  The  ultimate 
direction  of  motion  will,  according  to  our  theory  always 
be  such  that  the  mass  of  chemical  products  formed 
under  the  influence  of  Hght  in  symmetrical  photo- 
sensitive elements  during  the  same  time  is  equal. 

Patten  also  investigated  the  question  whether  the 
same  difference  of  percentage  between  two  lights  would 
give  the  same  deviation,  regardless  of  the  absolute 
intensities  of  the  lights  used.  The  absolute  intensity 
was  varied  by  using  in  turn  from  one  to  five  glowers. 
The  relative  intensity  between  the  two  lights  varied 
in  succession  by  0,  8}^,  16%,  25,  333^,  and  50  per 
cent.  Yet  the  angular  deflections  were  within  the 
limits  of  error  identical  for  each  relative  difference  of 
intensity  of  the  two  lights  no  matter  whether,  i,  2,  3, 
4,  or  5  glowers  were  used.  The  following  table  shows 
the  result. 


268       Animal  Instincts  and  Tropisms 

TABLE  IX 

A  Table  Based  on  the  Measurements  of  2700  Trails  Showing 

THE  Angular  Deflections  at  Five  Different  Absolute 

Intensities 


Number 

Difference  of  Intensity 

between  the  Two  Lights 

of 
Glowers 

0 

per  cent. 

8J3 
per  cent. 

per  cent. 

25 
per  cent. 

33}  3 
per  cent. 

50 
per  cent. 

I 
2 
3 
4 
5 

-0.55 

—  O.IO 

+0.45 

-0.025 

-0.225 

-2.32 

-3-05 
—2.60 
—2.98 
—2.92 

Deflection  in 

-5-27 

-6.12 

-5-65 
-6.60 

-5-125 

Degrees 
-9.04 
-8.55 
-8.73 
-9.66 
-8.30 

-11.86 

—  11.92 

-13-15 

—  11.76 

—  10.92 

-19.46 
-22.28 
-20.52 
-19.88 
-19.28 

Average 

—0.09 

-2.77 

-5-75 

-8.86 

—  11.92 

—20.28 

Such  constancy  of  quantitative  results  is  only 
possible  where  we  are  dealing  with  purely  physico- 
chemical  phenomena  or  where  life  phenomena  are 
unequivocally  determined  by  purely  physicochemical 
conditions. 

5.  It  seems  difficult  for  some  biologists,  even  with 
the  validity  of  the  Bunsen-Roscoe  law  proven,  to 
imagine  that  the  movements  of  the  animals  under  the 
influence  of  light  are  not  voluntary  (or  not  dictated  by 
the  mysterious  "trial  and  error"  method  of  Jennings).' 

'  According  to  this  theory  the  animal  is  not  directly  oriented  by  the 
outside  force,  e.  g.  the  light,  but  selects  among  its  random  movements  the 
one  which  is  most  "suited"  and  keeps  on  moving  in  this  direction.  This 
idea  is  untenable  for  most  if  not  all  the  cases  of  tropisms  and  has  been 


Animal  Instincts  and  Tropisms       269 

But  one  wonders  how  it  is  possible  on  such  an  assump- 
tion to  account  for  the  fact  that  the  angle  of  deflection 
of  the  larva  of  the  fly  when  under  the  influence  of  two 
lights  of  different  intensities  should  be  always  the  same 
for  a  given  difference  in  intensity;  or  why  the  time  for 
curvature  in  Eudendrium  should  vary  inversely  with 
the  intensity  of  illumination.  It  is,  however,  possible 
to  complete  the  case  for  the  purely  physicochemical 
analysis  of  these  instincts.  John  Hays  Hammond,  Jr., 
has  succeeded  in  constructing  hehotropic  machines 
which  in  the  dark  follow  a  lantern  very  much  in  the 
manner  of  a  positively  heliotropic  animal.  The  eyes 
of  this  heliotropic  machine  consist  of  two  lenses  in 
whose  focus  is  situated  the  "retina"  consisting  of 
selenium  wire.  The  two  eyes  are  separated  from 
each  other  by  a  projecting  piece  of  wood  which  re- 
presents the  nose  and  allows  one  eye  to  receive  light 
while  the  other  is  shaded.  The  galvanic  resistance  of 
selenium  is  altered  by  light;  and  when  one  selenium 
wire  is  shaded  while  the  other  is  illuminated,  the  elec- 
tric energy  (supplied  by  batteries  inside  the  machine) 
which  makes  the  wheels  turn  (these  take  the  place  of 

refuted  by  practically  all  the  workers  in  this  field,  e.  g.,  Parker  and  his 
pupils,  Bohn,  H.  B,  Torrey,  Holmes,  Bancroft,  Ewald,  and  others.  It  is 
only  upheld  by  Jennings  and  Mast;  and  Is  accepted  among  those  to 
whom  the  idea  of  a  physicochemical  explanation  of  life  phenomena  does 
not  appeal.  Torrey  and  Bancroft  (for  the  literature  the  reader  is  referred 
to  Bancroft's  paper,  Jozir.  Exper.  Zool.,  1913,  xv.,  383)  have  shown 
directly  that  the  theory  of  trial  and  error  is  not  even  correct  for  the 
organism  for  which  Jennings  has  developed  this  idea;  namely  Euglena. 


270       Animal  Instincts  and  Tropisms 

the  legs  of  the  normal  animal)  no  longer  flows  symmetri- 
cally to  the  steering  wheel,  and  the  machine  turns 
towards  the  light.  In  this  way  the  machine  follows 
a  lantern  in  a  dark  room  in  a  way  similar  to  that  of  a 
positively  heHotropic  animal.  Here  we  have  a  model 
of  the  heliotropic  animal  whose  purely  mechanistic 
character  is  beyond  suspicion,  and  we  may  be  sure 
that  it  is  not  "fondness"  for  hght  or  for  brightness 
nor  will-power  nor  a  method  of  "trial  and  error"  which 
makes  the  machine  follow  the  light. 

6.  It  may  also  be  of  interest  to  know  that  in  helio- 
tropism  the  motions  of  the  legs  are  automatically 
controlled  by  the  chemical  changes  taking  place  in 
S3^mmetrical  elements  of  the  retina.  In  order  to  prove 
this  point  we  will  turn  to  the  phenomenon  of  gal- 
vanotropism.  The  galvanic  current  forces  certain 
animals  to  move  in  the  direction  of  one  of  the  two 
electrodes  just  as  the  light  forces  the  heliotropic  animals 
to  move  towards  (or  from)  the  source  of  light.  The 
change  in  the  concentration  of  the  ions  at  the 
boundary  of  the  various  organs,  especially  the  nerves, 
determines  the  galvanotropic  reactions.  When  the 
shrimp  Palcemonetes  is  put  into  a  trough  with  dilute 
salt  solution  through  which  a  current  of  a  certain 
intensity  flows,  the  animal  is  compelled  to  move 
towards  the  anode.  ^  It  can  walk  forwards,  back- 
wards,   or  sidewise.     Here    we    can    observe   directly 

'  Loeb,  J.,  and  Maxwell,  S.  S.,  Arch.f.  d.  ges.  Physiol.,  1896,  Ixiii.,  121, 


Animal  Instincts  and  Tropisms       271 

that  the  effect  of  the  current  consists  in  altering  the 
tension  of  the  muscles  of  the  legs  in  such  a  way  as  to 
make  it  easy  for  the  animal  to  move  toward  the  anode 


Fig.  45 


and  difficult  to  move  toward  the  cathode.  Thus  if  the 
current  be  sent  sidewise  through  the  animal,  say  from 
left  to  right  (Fig.  45),  the  legs  of  the  left  side  assume  the 
flexor  position,  those  of  the  right  the  extensor  position. 
With  this  position  of  its  legs  the  animal  can  easily  move 


2']2       Animal  Instincts  and  Tropisms 

to  the  left,  i.  e.,  the  anode,  and  only  with  difficulty  to 
the  right,  i.  e.,  the  cathode.  This  change  in  the  position 
of  the  legs  occurs  when  the  animal  is  not  moving  at 
all,  thus  showing  that  the  galvanotropic  movements 
take  place  not  because  the  animal  intends  to  go  to 
the  anode,  but  that  the  animal  goes  to  the  anode  be- 
cause its  legs  are  practically  prevented  by  the  galvanic 
current  from  working  in  any  other  way.  This  is 
exactly  what  happens  in  the  heliotropic  motions  of 
animals.  ^ 

To  understand  what  happens  when  the  current  goes 
lengthwise  through  the  body  it  should  be  stated  that 
PalcBmonetes  uses  the  third,  fourth,  and  fifth  pairs  of 
legs  for  its  locomotion.  The  third  pair  pulls  in  the 
forward  movement,  and  the  fifth  pair  pushes.  The 
fourth  pair  generally  acts  like  the  fifth,  and  requires 
no  further  attention.  If  a  current  be  sent  through  the 
animal  longitudinally,  from  tail  to  head,  and  the  strength 
be  increased  gradually,  a  change  soon  takes  place  in 
the  position  of  the  legs  (Fig.  46).  In  the  third  pair  the 
tension  of  the  flexors  predominates,  in  the  fifth  the 
tension  of  the  extensors.  The  animal  can  thus  move 
easily  with  the  pulling  of  the  third  and  the  pushing 
of  the  fifth  pairs  of  legs,  that  is  to  say,  the  current 
changes  the  tension  of  the  muscles  in  such  a  way  that 

'  That  the  mechanisms  by  which  heliotropic  and  galvanotropic 
orientation  is  brought  about  are  identical  was  shown  by  Bancroft 
in  Euglena  (Bancroft,  loc.  cit.). 


Animal  Instincts  and  Tropisms        273 

the  forward  motion  is  rendered  easy,   the  backrv^ard 
motion  is  difficult.     Hence  it  can  easily  move  toward 


Fig.  46 


the  anode,  but  only  with  difficulty  toward  the  cathode. 
If  a  current  be  sent  through  the  animal  in  the  opposite 
direction,  namely,  from  head  to  tail,  the  third  pair 
of  legs  is  extended,  the  fifth  pair  bent ;  that  is,  the  third 


18 


274       Animal  Instincts  and  Tropisms 

pair  can  push,  and  the  fifth  pair  pull.  The  animal 
will  thus  move  backward  easily  and  forward  with 
difficulty,  and  it  is  thus  driven  to  the  anode  again. 

The  explanation  which  Loeb  and  Maxwell  proposed 
for  this  influence  of  the  current  on  the  legs  assumes 
that  there  are  three  groups  of  ganglion  cells  in  the 
central  nervous  system  of  these  animals  which  are 
oriented  according  to  the  three  main  axes  of  the  body; 
(i)  right-left  and  left-right,  (2)  backward,  and  (3)  for- 
ward. It  depends  upon  whether  the  ganglion  cells 
or  the  nerve  elements  are  in  anelectrotonus,  which 
muscles  are  bent  and  which  relaxed.  It  would  lead 
us  too  far  to  recapitulate  the  theory  in  this  place,  and 
the  reader  who  is  interested  in  it  is  referred  to  Loeb 
and  Maxwell's  paper,'  The  importance  of  the  ob- 
servations lies  in  the  fact  that  they  show  that  any 
element  of  will  or  choice  on  the  part  of  the  animal  in 
these  motions  is  eliminated,  that  the  animal  moves 
where  its  legs  carry  it,  and  not  that  the  legs  carry  the 
animal  where  the  latter  "wishes"  to  go. 

7.  This  may  be  the  place  to  dispel  an  error  which  has 
sometimes  crept  into  the  discussion  of  the  tropistic 
reactions  of  animals.  It  has  been  stated  occasionally 
that  it  is  the  energy  gradient  and  not  the  automatic 
orientation  of  the  animal  by  the  light  which  makes 
the  positively  heliotropic  animal  move  towards  the 
source  of  light  and  the  negatively  heliotropic  away 

'  Loeb,  J.,  and  Maxwell,  S.  S.,  Arch.f.  d.  ges.  Physiol.,  1896,  Ixiii.,  121. 


Animal  Instincts  and  Tropisms       275 


from  it.  Thus  the  positively  heliotropic  animal 
would  be  compelled  to  move  towards  the  source  of 
light  as  a  consequence  of  the  fact  that  the  intensity 
of  the  light  increases  the  more  the  nearer  the  animal 
approaches  the  source  of  light.  If  the  source  of  light 
be  the  reflected 
sky-light  the  dif- 
ference of  intensity 
at  both  ends  of  a 
microscopic  organ- 
ism is  so  slight 
that  it  is  beneath 
the  limit  capable 
of  influencing  the 
motions. 

A  simple  experi- 
ment published  by 
the  writer  in  1889 
suffices  to  dispel 
the  idea  that  the 

energy  gradient  determines  the  direction  of  the  mo- 
tion of  an  animal  in  tropistic  reactions.  Let  direct 
sunlight  (S,  Fig.  47)  fall  through  the  upper  half  of  a 
window  (w  w)  upon  a  table,  and  diffused  daylight  (D) 
through  the  lower  half  of  the  window  on  the  same 
table.  A  test-tube  a  c  is  placed  on  the  table  in  such  a 
way  that  its  long  axis  is  at  right  angles  to  the  plane 
of  the  window;  and  one  half  a  &  is  in  the  direct  sun- 


FiG.  47 


276       Animal  Instincts  and  Tropisms 

light,  the  other  half  in  the  shade.  If  at  the  be- 
ginning of  the  experiment  the  positively  heliotropic 
animals  are  in  the  direct  sunlight  at  a,  they  promptly 
move  toward  the  window,  gathering  at  the  window 
end  c  of  the  tube,  although  by  so  doing  they  go 
from  the  sunshine  into  the  shade.  ^  This  experi- 
ment is  in  harmony  with  our  idea  that  the  effect 
of  light  consists  in  turning  the  head  of  the  animal 
and  subsequently  its  whole  body  toward  the  source  of 
light.  By  going  from  the  strong  light  into  the  shade 
the  reaction  velocity  in  both  eyes  is  diminished  equally 
and  hence  there  is  no  reason  for  the  animal  to  change 
its  orientation,  though  its  progressive  motion  may  be 
stopped  for  an  instant  by  the  change.  But  at  the 
boundary  between  sunlight  and  daylight  a  sudden 
change  from  strong  to  weak  light  occurs.  If  the 
energy  gradient  determined  the  direction  of  the  posi- 
tively heliotropic  animal,  the  motion  should  stop  at 
the  boundary  from  strong  to  weak  light,  which  may 
happen  for  an  instant  but  which  will  not  interfere  with 
the  progressive  motion  of  the  animal. 

8.  Graber  had  found  that  when  animals  are  put  into 
a  trough  covered  half  with  blue  and  half  with  red  glass, 
those  that  are  "fond"  of  light  go  under  the  blue,  those 
that  are  "fond"  of  darkness  go  under  the  red  glass. 
The  writer  pointed  out  that  this  result  should  be 
expected  on  the  basis  of  his  theory  of  heliotropism,  if 

*  Loeb,  J.,  Dynamics  of  Living  Matter,  p.  126. 


Animal  Instincts  and  Tropisms        277 

the  assumption  be  correct  that  the  red  light  is  con- 
siderably less  efficient  than  light  which  goes  through 
blue  glass  (such  glass  also  allows  green  rays  to  go 
through).  The  botanists  had  already  shown  that  red 
glass  is  impermeable  for  the  rays  which  cause  helio- 
tropic  reactions  of  plants,  and  the  writer  was  able  to 
show  the  same  for  the  heliotropic  reactions  of  animals. 
Red  glass  acts,  therefore,  almost  like  an  opaque  body 
for  these  animals. 

A  closer  examination  of  the  most  efficient  rays  for 
the  heliotropic  reactions  of  different  organisms  has 
revealed  the  fact  that  for  some  organisms  a  region  in 
the  blue  ^  =  460— 490  ^;j.,  for  others  a  region  in  the 
yellowish-green,  near  about  X  =  520  —  530  jjljjl  Is  the  most 
efficient.^  For  many  plants  and  for  some  animals, 
like  Eudendrium  and  the  larvse  of  the  worm  Arenicola, 
a  region  in  the  blue  is  most  efficient;  for  certain,  if  not 
most,  animals  a  region  in  the  yellow-green  is  most 
efficient.  Among  unicellular  green  alg^,  Chlamydomo- 
nas,  has  its  maximal  efficiency  In  the  yellowish-green 
and  Euglena  in  the  blue.  According  to  observations 
by  Mast,  some  green  unicellular  organisms  like  Pan- 
dorina,  Eudorina,  and  Spondylomorum  seem  to  behave 
more  like  Chlamydomonas,  while  certain  others  behave 
more  like  Euglena .  ^   Wasteneys  and  the  writer  suggested 

'  Loeb,  J.,  and  Maxwell,  S.  S.,  Univ.  Cal.  Pub.,  1910,  Physiol.,  iii., 
195;  Loeb  and  Wasteneys,  Proc.  Nat.  Acad.  Sc,  1915,  i.,  44;  Science^ 
1915,  xH.,  328;  Jour.  Exper.  Zool.,  1915,  xix.,  23;  1916,  xx.,  217. 

'  Mast,  S.  O.,  Proc.  Nat.  Acad.  Sc,  1915,  i.,  622. 


2/8       Animal  Instincts  and  Tropisms 

that  there  are  two  groups  of  heliotropic  substances,  one 
with  a  maximum  of  photosensitiveness  in  the  blue,  the 
other  in  the  yellowish-green;  and  that  the  latter  group 
may  or  may  not  be  related  or  identical  with  the  visual 
purple  which  is  most  rapidly  bleached  by  light  of  a 
wave  length  near  X  =  520  — 530  \).\i. 

The  ophthalmologist  Hess^  has  utilized  the  helio- 
tropic reactions  of  animals  in  an  attempt  to  prove  that 
all  animals  from  the  lowest  invertebrates  up  to  the 
fishes  inclusive  suffer  from  total  colour-blindness.  This 
statement  was  based  on  the  observation  that  for  most 
positively  heliotropic  animals  the  region  in  the  yellowish- 
green  near  \  =  520  ^pi  seems  the  most  efficient.  Since 
this  region  of  the  spectrum  appears  also  as  the  brightest 
to  a  totally  colour-blind  man,  he  concluded  that  all 
these  animals  are  totally  colour-blind.  There  is  no 
reason  why  heliotropic  reactions  should  be  used  as  an 
indicator  for  colour  sensations;  if  totally  colour-blind 
human  beings  were  possessed  of  an  irresistible  impulse 
to  run  into  a  flame  Hess's  assumption  might  be  con- 
sidered, but  no  such  phenomenon  exists  in  colour- 
blind man.  Moreover,  v.  Frisch^  has  shown  by  ex- 
periments on  the  influence  of  the  background  on  the 
colouration  of  fish  as  well  as  by  experiments  on  bees  and 

'Hess,  C,  "Geslchtssinn,"  Winter  stein' s  Handb.  d.  vergl.  Physiol., 
1913,  iv. 

'v.  Frisch,  K.,  "Der  Farbensinn  und  Formensinn  der  Biene,"  Zool. 
Jahrh.  Abt.f.  allg.  Zool.  u.  Physiol.,  1914,  xxxv.  See  also  Ewald,  W.  F., 
Ztschr.  J.  SinnesphysioL,  1914,  xlviii.,  285. 


Animal  Instincts  and  Tropisms       279 

on  Daphnia  that  the  reactions  of  these  animals  to  light 
of  different  wave-lengths  indicate  different  effects 
besides  those  of  mere  intensity.  Thus  v.  Frisch  could 
train  bees  to  go  to  a  blue  piece  of  cardboard  distributed 
among  many  cardboards  of  different  shades  of  grey. 
Bees  thus  trained  would  alight  on  any  blue  object 
even  if  it  contained  no  food.  It  would  be  impossible 
to  do  this  with  totally  colour-blind  organisms. 

9.  Heliotropic  reactions  play  a  great  role  in  the 
preservation  of  individuals  as  well  as  of  species.  In 
order  to  understand  this  role  it  must  be  stated  that  the 
photosensitive  substances  appear  often  only  under  certain 
conditions  and  that  their  effect  is  inhibited  under  other 
conditions.  Thus  among  ants  the  winged  males  and 
females  alone  show  positive  heliotropism,  ^  while  the 
wingless  workers  are  free  from  this  reaction.  This 
positive  heliotropism  becomes  violent  at  the  time  of  the 
nuptial  flight  and  this  phenomenon  itself  seems  to  be  a 
heliotropic  phenomenon  since  it  takes  place  in  the 
direction  of  the  light.  When  the  queen  founds  her  nest 
she  loses  her  wings  and  becomes  negatively  heliotropic 
again.  Kellogg^  has  shown  that  the  nuptial  flight  of 
the  bees  is  also  a  purely  heliotropic  phenomenon. 
When  a  part  of  the  hive  remote  from  the  entrance  is 
illuminated  the  bees  rush  to  the  light  and  can  thus  be 
prevented  from  swarming.     These  phenomena  suggest 

'  Loeb,  J.,  Der  Heliotropismus  der  Tiere,  1889. 
2  Kellogg,  V.  L.,  Science,  1903,  xviii.,  693. 


28o       Animal  Instincts  and  Tropisms 

that  the  presence  of  some  substance  secreted  by  the 
sex  glands  may  cause  the  intensification  of  the  helio- 
tropism  which  leads  to  the  nuptial  flight. 

In  certain  species  of  Daphnia,  fresh-water  copepods, 
and  of  Volvox,  a  trace  of  CO  2  suffices  to  make  negatively 
heliotropic  or  indifferent  specimens  violently  positively 
heliotropic.  ^  Certain  forms  of  marine  copepods  and 
the  larvae  of  Polygordius  can  be  made  positively  helio- 
tropic by  lowering  the  temperature^  and  the  larvas  of 
the  barnacle  can  be  made  negatively  heliotropic  by 
strong  light.  ^  It  is  quite  possible  that  a  change  in  the 
sense  of  heliotropism  by  temperature  and  light  is  to 
some  extent  at  least  responsible  for  the  periodic  depth 
migrations  of  heliotropic  animals.  Many  if  not  all 
positively  heliotropic  animals  can  be  made  negatively 
heliotropic  by  exposure  to  ultra-violet  light.  "♦ 

A  most  interesting  example  of  the  r61e  of  heliotropism 
in  the  preservation  of  a  species  is  shown  in  the  cater- 
pillars of  Porthesia  chrysorrhcea.  The  butterfly  lays 
its  eggs  upon  a  shrub.  The  larvae  hatch  late  in  the  fall 
and  hibernate  in  a  nest  on  the  shrub,  as  a  rule  not  far 
from  the  ground.  As  soon  as  the  temperature  reaches 
a  certain   height,  they  leave  the  nest;  under  natural 

'  Loeb,  J.,  Arch.f.  d.  ges.  Physiol.,  1906,  cxv.,  564. 

'Ibid.,  1893,  liv.,  81. 

3  Groom,  Theo.  T.,  and  Loeb,  J.,  Biol.  Centralbl.,  1890,  x.,  160; 
Ewald,  W.  P.,  Jour.  Exper.  Zool.,  1912,  xiii.,  591. 

*  Loeb,  J.,  Arcli.  f.  d.  ges.  Physiol.,  1906,  cxv.,  564;  Moore,  A.  R., 
Jour.  Exper.  Zool.,  191 2,  xiii.,  573. 


Animal  Instincts  and  Tropisms       281 

conditions,  this  happens  in  the  spring  when  the  first 
leaves  have  begun  to  form  on  the  shrub.  (The  larvas 
can,  however,  be  induced  to  leave  the  nest  at  any  time 
in  the  winter  provided  the  temperature  is  raised  suffi- 
ciently.) After  leaving  the  nest,  they  crawl  directly 
upward  on  the  shrub  where  they  find  the  leaves  on 
which  they  feed.  Should  the  caterpillars  move  down 
the  shrub,  they  would  starve,  but  this  they  never  do, 
always  crawling  upward  to  where  they  find  their  food. 
What  gives  the  caterpillar  this  never-failing  certainty 
which  saves  its  life,  and  for  which  a  human  being 
might  envy  the  little  larva  ?  Is  it  a  dim  recollection  of 
experiences  of  former  generations?  It  can  be  shown 
that  it  is  the  light  reflected  from  the  sky  which  guides 
the  animal  upward.  When  we  put  these  animals  into  a 
horizontal  test-tube  in  a  room,  they  all  crawl  toward 
the  window,  or  toward  a  lamp ;  the  animal  is  positively 
heliotropic.  It  is  this  positive  heliotropism  which 
makes  them  move  upward  where  they  find  their  food, 
when  the  mild  air  of  the  spring  calls  them  forth  from 
their  nest.  At  the  top  of  the  branch,  they  come  in 
contact  with  a  leaf,  and  chemical  or  tactile  influences 
set  the  mandibles  of  the  young  caterpillar  into  activity. 
If  we  put  these  larvae  into  closed  test-tubes  which  lie 
with  their  longitudinal  axes  at  right  angles  to  the 
window,  they  will  all  migrate  to  the  window  end, 
where  they  stay  and  starve,  even  if  their  favourite  leaves 
are  close  behind  them.     They  are  slaves  of  the  light. 


282       Animal  Instincts  and  Tropisms 

The  few  young  leaves  on  top  of  a  twig  are  quickly 
eaten  by  the  caterpillar.  The  light,  which  saved  its 
life  by  making  it  creep  upward  where  it  finds  food, 
would  cause  it  to  starve  could  it  not  free  itself  from  the 
bondage  of  positive  heliotropism.  The  animal,  after 
having  eaten,  is  no  longer  a  slave  of  the  light,  but  can 
and  does  creep  downward.  It  can  be  shown  that  a 
caterpillar,  after  having  been  fed,  loses  its  positive 
heUotropism  almost  completely  and  permanently.  If 
we  submit  unfed  and  fed  caterpillars  of  the  same  nest 
contained  in  two  different  test-tubes  to  the  same 
artificial  or  natural  source  of  light,  the  unfed  will 
creep  to  the  light  and  stay  there  until  they  die,  while 
those  that  have  eaten  will  pay  little  or  no  attention 
to  the  Hght.  Their  sensitiveness  to  light  has  dis- 
appeared ;  after  having  eaten  they  become  independent 
of  Hght  and  can  creep  in  any  direction.  The  restlessness 
which  accompanies  the  condition  of  hunger  makes  the 
animal  creep  downward — which  is  the  only  direction 
open  to  it — where  it  finds  new  young  leaves  on  which 
it  can  feed.  The  wonderful  hereditary  instinct,  upon 
which  the  life  of  the  animal  depends,  is  its  positive 
heliotropism  in  the  unfed  condition  and  its  loss  of  this 
heliotropism  after  having  eaten.  The  latter  pheno- 
menon is  in  harmony  with  the  experiments  which  show 
that  the  heUotropism  of  certain  species  of  Daphnia 
disappears  when  the  water  becomes  neutral. 

And  finally  it  may  be  pointed  out  that  the  majority 


Animal  Instincts  and  Tropisms       2S3 

of  green  plants  could  not  exist  if  their  stems  were  not 
positively,  their  roots  negative^,  heHotropic.  It  is 
the  positive  heHotropism  which  makes  the  top  grow 
toward  the  hght,  which  enables  the  leaves  to  get  the 
light  necessar}^  for  assimilation,  and  the  roots  to  grow 
into  the  soil  where  they  find  the  water  and  nutritive 
salts. 

10.  While  we  do  not  wish  to  deal  here  with  the 
different  tropisms  it  should  be  stated  that  aside  from 
heUotropism,  chemotropism  as  well  as  stereotropism 
pla}'  the  most  essential  role  in  the  so-called  instinctive 
actions  of  animals.  It  is  a  problem  of  orientation  by 
the  diffusion  of  molecules  from  a  centre  when  a  male 
butterfly  is  deviated  from  its  flight  and  ahghts  on  the 
wooden  box  in  which  is  enclosed  a  female  of  the  same 
species.  We  have  already  alluded  to  certain  phenomena 
of  chemotropism  in  Chapter  IV.  Certain  organisms 
have  a  tendency  to  bring  their  bodies  as  much  as 
possible  on  all  sides  in  contact  with  soHd  bodies;  thus 
the  butterfly  AmpMpyra,  which  is  a  fast  runner, 
win  come  to  rest  under  a  glass  plate  when  the  plate 
is  put  high  enough  above  the  ground  so  that  it  touches 
the  back  of  the  butterfly.  The  animals  which  live 
under  stones  or  underground  or  in  caves  are  as  a  rule 
both  negatively  heHotropic  and  positively  stereotropic. 
Their  tropisms  predestine  or  force  them  into  the  life 
they  lead. 

The  sensitive  area  which  forms  the  basis  of  tropisms 


284       Animal  Instincts  and  Tropisms 

is  as  a  rule  developed  not  in  the  whole  organism  but 
only  in  certain  segments  of  the  body.  Thus  the  eyes 
are  located  in  the  head.  But  when  the  action  of 
one  segment  becomes  overpowering  the  whole  or- 
ganism follows  the  segment.  It  has  been  customary 
among  physiologists  to  speak  of  reflexes  in  such  cases. 
Thus,  e.  g.,  the  arms  of  the  male  frog  develop  a  powerful 
positive  stereotropism  on  their  ventral  surface  during 
the  spawning  season.  It  would  avoid  confusion  to 
realize  that  there  is  nothing  gained  in  applying  to  this 
tropism  the  meaningless  term  "reflex";  it  is  better  to 
call  them  tropisms  since  the  organism  as  a  whole  is 
involved.  If  necessary  we  might  speak  of  segmental 
tropisms.  The  act  of  seeking  the  female  as  well  as 
that  of  cohabitation  are  in  many  cases  combinations 
of  chemotropism  and  stereotropism.  The  development 
of  these  tropisms  depends  upon  the  presence  of  certain 
specific  substances  in  the  body,  a  fact  emphasized 
already  in  the  case  of  heliotropism.  In  case  of  the 
development  of  the  segmental  stereotropism  of  the  male 
frog  at  the  time  of  spawning  it  has  been  shown  that  it 
depends  on  an  internal  secretion  from  the  testes. 

It  has  been  suggested  by  some  authors  that  the 
tropistic  reactions  are  determined  by  some  feeling  or 
emotion  on  the  part  of  the  organism.  We  have  no 
means  of  judging  the  emotions  of  lower  animals  (except 
by  "intuition").  The  writer  suggested  in  1899  in  his 
book  on  brain  physiology  that  emotions  may  be  deter- 


Animal  Instincts  and  Tropisms       285 

mined  by  specific  substances  which  also  determine 
the  tropistic  reaction  (as  well  as  phenomena  of  organ 
formation,  although  this  latter  phenomenon  has 
nothing  to  do  with  the  subject  of  instincts) ;  and  the 
excellent  work  of  Cannon^  has  shown  the  role  of  adre- 
nalin in  the  expression  of  fear.  It  is,  therefore,  both 
unwarranted  and  unnecessary  to  state  that  hypotheti- 
cal emotions  determine  the  tropistic  reactions. 

'  Cannon,  W.  B.,  Bodily  Changes  in  Pain,  Hunger,  Fear,  and  Rage, 
New  York,  19 15. 


CHAPTER  XI 

THE  INFLUENCE  OF  ENVIRONMENT 

I .  The  term  environment  in  relation  to  an  organism 
may  easily  assume  a  mystic  role  if  we  assume  that  it 
can  modify  the  organisms  so  that  they  become  adapted 
to  its  peculiarities.  Such  ideas  are  difficult  to  compre- 
hend from  a  physicochemical  viewpoint,  according  to 
which  environment  cannot  affect  the  living  organism 
and  non-living  matter  in  essentially  different  ways. 
Of  course  we  know  that  proteins  will  as  a  rule  coagulate 
at  temperatures  far  below  the  boiling  point  of  water 
and  that  no  life  is  conceivable  for  any  length  of  time 
at  temperatures  above  ioo°  C,  but  heat  coagulation  of 
proteins  occurs  as  well  in  the  test-tube  as  in  the  living 
organism.  If  we  substitute  for  the  indefinite  term 
environment  the  individual  physical  and  chemical 
forces  which  constitute  environment  it  is  possible  to 
show  that  the  influence  of  each  of  these  forces  upon  the 
organism  finds  its  expression  in  simple  physicochemical 
laws  and  that  there  is  no  need  to  introduce  any  other 

considerations. 

286 


The  Influence  of  Environment        2^,^ 

We  select  for  our  discussion  first  the  most  influential 
of  external  conditions,  namely  temperature.  The 
reader  knows  that  there  is  a  lower  as  well  as  an  upper 
temperature  limit  for  life.  Setchell  has  ascertained 
that  in  hot  springs  whose  temperature  is  43°  C,  or 
above,  no  animals  or  green  alg^  are  found.  ^  In  hot 
springs  whose  temperature  is  above  43°  he  found 
only  the  CyanophycecB,  whose  structure  is  more  closely 
related  to  that  of  the  bacteria  than  to  that  of  the  alg£e, 
inasmuch  as  they  have  neither  definitely  differentiated 
nuclei  nor  chromophores.  The  highest  temperature 
at  which  Cyanophycece  occurred  was  63°  C.  Not  all  the 
CyanophycecB  were  able  to  stand  temperatures  above 
43°  C,  but  only  a  few  species.  The  other  Cyanophycece 
were  found  at  a  temperature  below  40°  C,  and  were  no 
more  able  to  stand  higher  temperatures  than  the  real 
algae  or  animals.  The  Cyanophycece  of  the  hot  springs 
were  as  a  rule  killed  by  a  temperature  of  73°.  From 
this  we  must  conclude  that  they  contain  proteins  whose 
coagulation  temperature  lies  above  that  of  animals 
and  green  plants,  and  may  be  as  high  as  73°.  Among 
the  fungi  many  forms  can  resist  a  temperature  above 
43°  or  45°;  the  spores  can  generally  stand  a  higher 
temperature  than  the  vegetative  organs.  Duclaux 
found  that  certain  bacilli  (Tyrothrix)  found  in  cheese 
are  killed  in  one  minute  at  a  temperature  of  from  80° 

'  Setchell,  W.  A.,  Science,  1903,  xxvii.,  934. 


288        The  Influence  of  Environment 

to  90°;  while  for  the  spores  of  the  same  bacillus  a 
temperature  of  from  105°  to  120°  was  required.^ 

Duclaux  has  called  attention  to  a  fact  which  is  of 
importance  for  the  investigation  of  the  upper  tempera- 
ture limit  for  the  life  of  organisms.  According  to  this 
author  it  is  erroneous  to  speak  of  a  definite  temperature 
as  a  fatal  one;  instead  we  must  speak  of  a  deadly 
temperature  zone.  This  is  due  to  the  fact  that  the 
length  of  time  which  an  organism  is  exposed  to  a  higher 
temperature  is  of  importance.  Duclaux  quotes  as  an 
example  a  series  of  experiments  by  Christen  on  the 
spores  of  soil  and  hay  bacilli.  The  spores  were  exposed 
to  a  stream  of  steam  and  the  time  determined  which 
was  required  at  the  various  temperatures  to  kill  the 
spores. 

It  took  at  lOo"' over  sixteen  hours 

"       "     "   105-110" two  to  four  hours 

"       "     "  115" thirty  to  sixty  minutes 

"       "     "  125-130° five  minutes  or  more 

"       "     "  135° one  to  five  minutes 

"       "     "  140° one  minute 

In  warm-blooded  animals  45°  is  generally  considered 
a  temperature  at  which  death  occurs  in  a  few  minutes; 
but  a  temperature  of  44°,  43°,  or  42°  is  also  to  be 
considered  fatal  with  this  difference  only,  that  it  takes 

*  Duclaux,  E.,  Traits  de  microhiol.,  1898,  i.,  280. 


The  Influence  of  Environment        289 

a  longer  time  to  bring  about  death.  This  fact  is  to  be 
considered  in  the  treatment  of  fever. 

It  is  generally  held  that  death  in  these  cases  is  due 
to  an  irreversible  heat  coagulation  of  proteins.  Ac- 
cording to  Duclaux,  it  can  be  directly  observed  in 
micro-organisms  that  in  the  fatal  temperature  zone 
the  normally  homogeneous,  or  finely  granulated,  proto- 
plasm is  filled  with  thick,  irregularly  arranged  bodies, 
and  this  is  the  optical  expression  of  coagulation.  The 
fact  that  the  upper  temperature  limit  differs  so  widely 
in  different  forms  is  explained  by  Duclaux  through 
differences  in  the  coagiilation  temperature  of  the  various 
proteins.  It  is,  e.  g.  known  that  the  coagulation 
temperature  varies  with  the  amount  of  water  of  the 
colloid.  According  to  Cramer,  the  mycelium  of  Peni- 
cillium  contains  87.6  water  to  12.4  dry  matter,  while 
the  spores  have  38.9  water  and  61. i  dry  substance. 
This  may  explain  why  the  mycelium  is  killed  at  a 
lower  temperature  than  the  spores.  According  to 
Chevreul,  with  an  increase  in  the  amount  of  water, 
the  coagulation  temperature  of  albuminoids  decreases. 
The  reaction  of  the  protoplasm  influences  the  tempera- 
ture of  coagulation,  inasmuch  as  it  is  lower  when  the 
reaction  is  acid,  higher  when  the  reaction  is  alkaline. 
The  experiments  of  Pauli  show  also  a  marked  influence 
of  salts  upon  the  temperature  of  coagulation  of  colloids. 

The  process  of  heat  coagulation  of  colloids  is  also  a 
function  of  time.     If  the  exposure  to  high  temperature 


290        The  Influence  of  Environment 

is  not  sufficiently  long,  only  part  of  the  colloid  coagulates ; 
in  this  case  an  organism  may  again  recover. 

Inside  of  these  upper  and  lower  temperature  limits 
we  find  that  life  phenomena  are  influenced  by  tempera- 
ture in  such  a  way  that  their  rate  is  about  doubled  for 
an  increase  of  the  temperature  of  io°  C,  and  that  this 
temperature  coefficient  for  io°,  Q^o,  very  often  steadily 
diminishes  from  the  lower  to  the  higher  temperature; 
so  that  near  the  lower  temperature  limit  it  becomes 
often  considerably  greater  than  2  and  near  the  higher 
temperature  limit  it  becomes  very  often  less  than  2.^ 
This  influence  of  temperature  is  so  general  that  we  are 
bound  to  associate  it  with  an  equally  general  feature  of 
life  phenomena;  and  such  a  feature  would  be  most 
likely  the  chemical  reactions.  It  is  known  through  the 
work  of  Berthelot,  van't  Hoff,  and  Arrhenius  that  the 
temperature  coefficient  for  the  velocity  of  chemical 
reactions  is  also  generally  of  about  the  same  order  of 
magnitude;  namely  ^  2  for  a  difference  of  io°.  In 
chemical  reactions  there  is  also  a  tendency  for  Qio  to 
become  larger  for  lower  temperature,  and  coefficients 
of  Qio  about  5  or  6  have  repeatedly  been  found  for 
purely  chemical  reactions  between  o°  and  io°,  e.  g., 
for  the  inversion  of  cane  sugar  by  the  hydrogen  ion. 
The  temperature  coefficient  for  the  reaction  velocity 
of  ferments  shows  the  same  diminution    of  Qxo  with 

'  A  full  discussion  of  the  literature  on  temperature  coefficients  is  given 
in  A.  Kanitz's  book  on  Temperatur  und  Lebensvorgdnge,  Berlin,  1915. 


The  Influence  of  Environment        291 

rising  temperature  which  is  also  noticed  in  most  life 
phenomena.  Thus  Van  Slyke  and  Cullen^  found  that 
the  reaction  rate  of  the  enzyme  urease  "is  nearly 
doubled  by  every  10°  rise  in  temperature  between  10° 
and  50°.  Within  this  range  the  temperature  coefficient 
is  nearly  constant  and  averages  1.9 1.  From  0°  to  10°  it 
is  2.80,  from  50°  to  60°  it  is  only  1.09.  The  optimum 
is  at  about  55°."  The  rapid  fall  of  the  temperature 
coefficient  for  enzyme  action  at  the  upper  temperature 
limit  has  been  ascribed  by  Tammann  to  a  progressive 
destruction  of  the  active  mass  of  enzyme  by  the  higher 
temperature  (by  hydrolysis).  This  will,  however,  not 
account  for  the  high  value  of  the  coefficient  near  the 
lower  limit.  But  is  it  not  imaginable  that  at  low 
temperature  an  aggregation  of  the  enzyme  particles 
exists  which  is  also  equivalent  to  a  diminution  of  the 
active  mass  of  the  enzyme  and  that  this  aggregation  is 
gradually  dispersed  by  the  rising  temperature?  This 
would  account  for  the  fact  that  at  a  temperature  near 
o°C  life  phenomena  stop  because  the  enzymes  are  all 
in  a  state  of  aggregation  or  gelation;  that  then  more 
and  more  are  dissolved  and  the  rate  of  chemical  re- 
action increases  since  the  mass  of  enzyme  particles 
increases  until  all  the  enzyme  molecules  are  dissolved 
or  rendered  active.  Under  this  assumption  three 
processes  are  superposed  in  the  variation  of  the  value 

'  Van  Slyke,  D.  D.,  and  Cullen,  G.  E.,  Jour.  Biol.  Chem.,  1914,  xix., 
141. 


292        The  Influence  of  Environment 

of  Qio  with  temperature:  (i)  the  supposed  increase  in 
the  number  of  available  ferment  molecules  with  in- 
creasing temperature  near  the  lower  temperature  limit ; 
(2)  the  temperature  coefficient  of  the  reaction  velo- 
city which  is  nearly  =  2  for  io°C. ;  (3)  the  diminution 
of  the  number  of  available  ferment  molecules  by  hydroly- 
sis or  some  other  action  of  the  increasing  temperature. 
This  latter  is  noticeable  near  the  upper  temperature 
limit.  The  reason  that  i  and  3  interfere  more  strongly 
in  life  phenomena  than  in  the  chemical  reactions  of 
crystalloid  substances  may  possibly  be  accounted  for 
by  the  fact  that  the  enzymes  and  most  of  the  con- 
stituents of  living  matter  are  colloidal,  i.  e.,  consist  of 
particles  of  a  considerably  greater  order  of  magnitude 
than  the  molecules  of  crystalloids. ' 

We  will  now  show  the  role  of  the  temperature 
coefficient  upon  phenomena  of  development.  F.  R. 
Lillie  and  Knowlton^  first  determined  the  influence  of 
temperature  upon  the  development  of  the  egg  of  the 
frog  and  showed  that  it  was  of  the  same  nature  as  that  of 
a  chemical  reaction.  These  experiments  were  repeated 
a  year  later  by  0.  Hertwig.^ 

'  These  considerations  may  meet  the  objections  of  Krogh  to  the 
application  of  the  van't  Hoff  rule  of  temperature  effect  on  reaction 
velocity  to  life  phenomena.  See  also  the  discussion  of  this  subject  in 
Kanitz's  book. 

'  Lillie,  F.  R.,  and  Knowlton,  E.  P.,  Zool.  Bull.,  1897,  i. 

^Hertwig,  O.,  Arch,  mikrosk.  Anat.,  1898,  H.,  319.  See  also  E. 
Cohen,  Vortrdge  jilr  Aerzte  uber  physikalische  Chemie.  2d  ed.  Leip-. 
zig,  1907. 


The  Influence  of  Environment        293 

The  time  required  for  the  eggs  to  reach  definite 
stages  was  measured  for  different  temperatures  and 
it  was  found  that  the  temperature  coefficient  Qio 
between  2.5°  and  6°  was  equal  to  10  or  more;  between 
6°  and  15°  it  was  between  2.6  and  4.5;  between  10°  and 
20°  it  was  2.9  to  3.3,  and  between  20^  and  24^  it  was 
between  1.4  and  2.0.  To  anybody  who  has  worked 
on  this  problem  it  is  obvious  that  no  exact  figures 
can  be  obtained  in  this  way,  since  the  point  when 
a  certain  stage  of  development  is  reached  is  not 
so  sharply  defined  as  to  exclude  a  certain  latitude  of 
arbitrariness.  The  writer  found  that  very  exact 
figures  can  be  obtained  on  the  influence  of  temperature 
upon  development  of  the  sea-urchin  egg  by  measuring 
the  time  from  insemination  to  the  first  cell  division. 
Such  experiments  were  carried  out  in  a  cold-water  form 
Strongylocentrotus  purpuratiis  and  a  form  living  in 
warmer  water,  Arhacia.''  The  fi.gures  on  Arhacia 
have  been  verified  by  different  observers  in  different 
years. 

^  Loeb,  J.,  Arch.  f.  d.  ges.  Physiol.,  1908,  cxxiv.,  411;  Loeb  J.,  and 
Wasteneys,  H.,  Biochem.  Ztschr.,  191 1,  xxx^-i.,  345;  Loeb  J.,  and  Cham- 
berlain, M.  M.,  Jour.  Exper.  Zodl.,igi^,  six.,  559. 


294       The  Influence  of  Environment 

TABLE  X 

Influence  of  Temperature  upon  the  Time  (in  Minutes)  Required 
FROM  Insemination  to  the  First  Cell  Division 


1 
1 

Arbacia 

Tempera- 

Strongylocentrotus 

:        TURE 

LOEB  AND 

Loeb  and 

purpuratus 

I- 

Wasteneys 

Chamberlain 

I9II 

1915 

°c. 

Alitiutes 

Minutes 

Minutes 

3 

532 

4 

469 

5 

352 

6 

275 

7 

498 

291 

8 

410 

411 

210 

9 

308 

297-5 

159 

ID 

217 

208 

143 

II 

175 

175 

12 

147 

148 

131 

13 

129 

14 

116 

121 

15 

100 

100 

100 

i6 

85.5 

17 

70.5 

l8 

68 

68 

87 

19 

65 

78 

20 

56 

56 

75 

21 

53-3 

78 

22 

47 

46 

75 

23 

45-5 

Upper  tempera- 

24 

42 

ture  limit 

25 

40 

39-5 

26 

33-5 

27-5 

34 

30 

33 

31 

37 

These  figures  permitted  the  determination  of  the 
temperature  coefficients  Q^,  with  a  sufficient  degree  of 
accuracy  (see  next  table).     It  seemed  of  importance 


The  Influence  of  Environment       295 


to  attempt  to  decide  what  the  chemical  reaction  under- 
lying these  reaction  velocities  is  (if  it  is  a  chemical 
reaction).  Loeb  and  Wasteneys^  investigated  the 
temperature  coefficient  for  the  rate  of  oxidations  in 
the  newly  fertilized  egg  of  Arhacia  and  found  that  the 
temperature  coefficient  Qio  for  that  process  does  not 
vary  in  the  same  way  as  the  temperature  coefficient 
for  cell  division. 

TABLE  XI 

Temperature  Coefficients  Qio  for  the  Rate  of  Segmentation 

AND    Oxidations   in   the   Eggs   of   Strongylocentrotiis 

and  Arbacia 


Qio  for  Rate  of  Segmentation  in 

Qio  for  Rate  of   . 
Oxidations    in 

Temperature 

Arbacia 

Strongylocentrotus 

A rbacia 

°C. 

3-13 

391 

2.18 

4-14 

3-88 

5-15 

3-52 

2.16 

7-17 

3-27 

7-3 

2.00 

8-18 

6.0 

9-19 

2.04 

4-7 

10-20 

1.90 

3-8 

2.17 

1 1-2 1 

3-3 

12-22 

1.74 

3-1 

13-23 

2.8 

2.45 

15-25 

2-5 

2.24 

16-26 

2.6 

I7-5-27-5 

2.2 

2.00 

20-30 

1-7 

1.96 

It  is  obvious  that  the  temperature  coefficient  of 
the  rate  of  oxidations  is  remarkably  constant,  about 
2  for  10°,  for  various  temperatures  and  does  not  show 

*  Loc.  cit. 


296        The  Influence  of  Environment 

the  variation  from  7  or  more  to  2.2  for  Q  jo  for  the  rate  of 
segmentation. 

Kanitz^  has  shown  that  in  a  graph  in  which  the 
logarithms  of  the  segmentation  velocities  are  drawn 
as  ordinates  and  the  temperatures  as  abscissae  the 
logarithms  form  two  straight  lines  which  are  joined  at 
an  angle.  According  to  the  law  of  van't  Hoff  and 
Arrhenius  concerning  the  influence  of  temperature  upon 
velocities  of  chemical  reactions  the  logarithms  should 
lie  in  a  straight  line.  We  are  dealing  therefore  in  these 
cases  with  two  exponential  curves,  one  representing  in 
Arbacia  the  interval  7-13°  and  the  second  from  13-26°; 
in  Strongylocentrotus  between  3-9°  and  9-20°. 

It  was  found  in  these  experiments  that  if  measure- 
ments of  the  Qio  of  later  stages  of  development  are 
attempted  the  variations  due  to  unavoidable  difficulties 
become  too  great  to  permit  an  equal  degree  of  reliability 
in  the  determinations. 

The  vast  importance  of  this  influence  of  temperature 
upon  the  rate  of  development  is  seen  in  the  fact  that  in 
addition  to  the  food  supply  the  rate  of  the  maturing 
of  plants  and  animals  depends  on  this  factor. 

2.  This  influence  of  temperature  upon  develop- 
ment has  been  used  to  find  the  conditions  determining 
fluctuating  variation.  The  reader  knows  that  by  this 
expression  are  understood  the  differences  between  in- 
dividuals of  a  pure  strain  or  breed.     These  variations 

'  Kanitz,  A.,  loc.  ciL,  p.  123. 


The  Influence  of  Environment       297 

are  not  inherited,  a  fact  contrary  to  the  idea  of  Dar- 
win, who  assumed  that  by  the  selection  of  extreme 
cases  of  fluctuating  variation  new  varieties  could  de- 
velop. What  is  the  basis  of  this  fluctuating  variation? 
The  writer  concluded  that  if  fluctuating  variations 
were  due  to  a  slight  variation  in  the  quantity  of  a 
specific  substance — in  some  cases  an  enzyme — required 
for  the  formation  of  a  hereditary  character,  the  tem- 
perature coefScient  might  be  used  to  test  the  idea.  We 
have  just  seen  that  the  time  required  from  insemina- 
tion until  the  cell  division  of  the  first  egg  occurs  is 
very  sharply  defined  for  each  temperature.  If  a  large 
number  e.g.  one  hundred  or  more  eggs  are  under  obser- 
vation simultaneously  in  a  microscopic  field  it  can  be 
seen  that  they  do  not  all  segment  at  the  same  time 
but  in  succession;  this  is  the  expression  of  fluctuating 
variation.  Miss  Chamberlain  and  the  writer  have 
measured  the  time  which  elapses  between  the  moment 
the  first  egg  of  such  a  group  segments  and  the  moment 
the  last  egg  begins  its  segmentation,  and  found  that  this 
latitude  of  variation  is  also  very  definite  for  each  tem- 
perature, and  that  its  temperature  coefficient  is  for 
each  interval  of  10°  practically  identical  with  the 
temperature  coefficient  of  the  segmentation  for  the 
same  interval.^  The  slight  deviations  are  practically 
all  in  the  same  sense  and  accounted  for  by  a  slight 
deficiency   in    the    nature    of    the    experiments.     The 

'  Loeb,  J.,  and  Chamberlain,  M.  M.,  Jour.  Exper.  ZooL,  1915,  xix.,  559. 


298        The  Influence  of  Environment 


two  following  tables  give  the  latitude  of  variations  for 
different  temperatures  for  the  first  segmentation  in 
Arbacia  and  the  temperature  coefficient  for  this  latitude 
and  the  rate  of  segmentation.  These  two  latter  co- 
efficients are  practically  identical. 

TABLE  XII 


Latitude 

Latitude 

Temperature 

of 

Temperature 

of 

Variation 

Variation 

°C. 

Minutes 

°C. 

Minutes 

9 

52.5 

18 

12.0 

10 

39-5 

19 

12.5 

II 

26.0 

20 

9.6 

12 

22.5 

21 

8.0 

13 

19.2 

22 

7.8 

14 

17-5 

23 

8.0 

15 

13.0 

24 

8.0 

25 

50 

TABLE  XIII 


TEMPERATURE   COEFFICIENT    OF 

Temperature 
Interval 

Latitude 
Variation 

Segmentation 

°C. 

9-19 
10-20 

II-2I 
12-22 

13-23 
14-24 

15-25 

4.2 

3-9 
3-2 
2.8 
2.4 

2.3 
2.6 

4-7 
3.8 
3-3 
31 
2.8 
2.8 

2-5 

The  Influence  of  Environment       299 

If  we  assume  that  the  temperature  coefficient  for 
the  segmentation  of  the  egg  is  that  of  a  chemical  re- 
action (other  than  oxidation)  underlying  the  process 
of  segmentation,  the  fluctuating  variation  in  the  time 
of  the  segmentations  of  the  various  eggs  fertilized  at  the 
same  time  is  due  to  the  fact  that  the  mass  of  the  enzyme 
controlling  that  reaction  varies  within  definite  limits 
in  different  eggs.  The  first  egg  segmenting  at  a  given 
temperature  has  the  maximal,  the  last  egg  segmenting 
has  the  minimal  mass  of  enzyme.  It  should  be  added 
that  the  time  of  the  first  segmentation  is  determined  by 
the  cytoplasm  and  is  not  a  Mendelian  character,  as 
was  stated  in  a  previous  chapter. 

3.  The  point  of  importance  to  us  is  that  the  influ- 
ence of  temperature  upon  the  organism  is  so  constant 
that  if  disturbing  factors  are  removed  it  would  be  pos- 
sible to  use  the  time  from  insemination  to  the  first 
segmentation  of  an  egg  of  Arhacia  as  a  thermometer 
on  the  basis  of  the  table  on  page  295. 

Facts  of  this  character  should  dispose  of  the  idea 
that  the  organism  as  a  whole  does  not  react  with  that 
degree  of  machine-like  precision  which  we  find  in  the 
realm  of  physics  and  chemistry.  Such  an  idea  could 
only  arise  from  the  fact  that  biologists  have  not  been 
in  the  habit  of  looking  for  quantitative  laws,  chiefly, 
perhaps,  because  the  difficulties  due  to  disturbing 
secondary  factors  were  too  great.  The  worker  in 
physics  knows  that  in  order  to  discover  the  laws  of  a 


300        The  Influence  of  Environment 

phenomenon  all  the  disturbing  factors  which  might 
influence  the  result  must  first  be  removed.  When  the 
biologist  works  with  an  organism  as  a  whole  he  is 
rarely  able  to  accomplish  this  since  the  various  dis- 
turbing influences,  being  inseparable  from  the  life  of 
the  organism,  can  often  not  be  entirely  removed.  In 
this  case  the  biologist  must  look  for  an  organism  in 
which  by  chance  this  elimination  of  secondary  condi- 
tions is  possible.  The  following  example  may  serve 
as  an  illustration  of  this  rather  important  point  in 
biological  work.  Although  all  normal  human  beings 
have  about  the  same  temperature,  yet  if  the  heart- 
beats of  a  large  number  of  healthy  human  beings  are 
measured  the  rate  is  found  to  vary  enormously.  Thus 
V.  Korosy  found  among  soldiers  under  the  most  favour- 
able and  most  constant  conditions  of  observations — 
the  soldiers  were  examined  early  in  the  morning  before 
rising — variations  in  the  rate  of  heart-beat  between 
42  and  108.  In  view  of  this  fact,  those  opposed  to  the 
idea  that  the  organism  as  a  whole  obeys  purely  physico- 
chemical  laws  might  find  it  preposterous  to  imagine  that 
the  rate  of  heart-beat  could  be  used  as  a  thermometer. 
Yet  if  we  observe  the  influence  of  temperature  on  the 
rate  of  the  heart-beat  of  a  large  number  of  embryos  of 
the  fish  Fundulus,  while  the  embryos  are  still  in  the 
egg,  we  find  that  at  the  same  temperature  each  heart 
beats  at  the  same  rate,  the  deviations  being  only 
slight  and   such  as   the  fluctuating  variations  would 


The  Influence  of  Environment       301 

demand.^  This  constancy  is  so  great  that  the  rate 
of  heart-beat  of  these  embryos  could  in  fact  be  used 
as  a  rough  thermometer.  The  influence  of  tempera- 
ture upon  the  rate  of  heart-beat  is  completely  reversible 
so  that  when  we  measure  the  rate  for  increasing  as  well 
as  for  decreasing  temperatures  we  get  approximately 
the  same  values  as  the  following  table  shows. 

TABLE  XIV 


Temperature 

Time  Regiiired  fcr  Nineteen  Heart-heats  in 
the  Embryo  of  Fundulus 

°C. 

Seconds 

30 

6.25 

25 

8.5 

20 

II-5 

15 

19.0 

10 

32.5 

5 

61.0 

10 

33-5 

15 

18.8 

20 

12.0 

25 

lO.O 

30 

6.0 

Why  does  each  embryo  have  the  same  rate  of  heart- 
beat at  the  same  temperature  in  contradistinction  to 
the  enormous  variability  of  the  same  rate  in  man? 
The  answer  is,  on  account  of  the  elimination  of  all 
secondary  disturbing  factors.  In  the  embryo  of  Fun- 
dulus the  heart-beat  is  a  function  almost  if  not  exclu- 

^  Loeb,  J.,  and  Ewald,  W.  F.,  Biochem.  Ztschr.,  1913,  Iviii.,  179. 


302       The  Influence  of  Environment 

sively  of  two  variables,  the  mass  of  enzymes  for  the 
chemical  reactions  underiying  the  heart-beat  and  the 
temperature.  By  inheritance  the  mass  of  enzymes  is 
approximately  the  same  and  in  this  way  all  the  embryos 
beat  at  the  same  rate  (within  the  limits  of  the  fluctuat- 
ing variation)  at  the  same  temperature.  This  identity 
exists,  however,  only  as  long  as  the  embryo  is  relatively 
quiet  in  the  egg.  As  soon  as  the  embryo  begins  to 
move  this  equality  disappears  since  the  motion  influ- 
ences the  heart-beat  and  the  motility  of  different 
embryos  differs. 

In  man  the  number  of  disturbing  factors  is  so 
great  that  no  equality  of  the  rate  for  the  same  tem- 
perature can  be  expected.  Differences  in  emotions 
or  the  internal  secretions  following  the  emotions, 
differences  in  previous  diseases  and  their  after-effects, 
differences  in  metabolism,  differences  in  the  use  of 
narcotics  or  drugs,  and  differences  in  activity  are  only 
some  of  the  number  of  variables  which  enter. 

4.  As  stated  above  the  temperature  influences 
practically  all  life  phenomena  in  a  similar  characteristic 
way,  e.  g.,  the  production  of  CO  2  in  seeds  ^  and  the 
assimilation  of  CO2  by  green  plants.^  The  writer 
would  not  be  surprised  if  even  the  aberrations  in  the 
colour  of  butterflies  under  the  influence  of  temperature 

^  Clausen,  H.,  Landwirtschaftl.  Jahrb.,  1890,  xlx.,  893. 
'  Matthaei,  G.  L.  C,  Trans.  Philosoph.  Soc,  1904,  cxcvii.,  47;  Black- 
pian  F,  F.,  Ann.  of  BoL,  1905,  xix.,  281, 


The  Influence  of  Environment       303 

turned  out  to  be  connected  with  the  temperature  co- 
efficient. The  experiments  of  Dorfmeister,  Weismann, 
Merrifield,  Standfuss,  and  Fischer,  on  seasonal  dimor- 
phism and  the  aberration  of  colour  in  butterflies  have 
so  often  been  discussed  in  biological  literature  that  a 
short  reference  to  them  will  suffice.  By  seasonal 
dimorphism  is  meant  the  fact  that  species  may  appear 
at  different  seasons  of  the  year  in  a  somewhat  different 
form  or  colour.  Vanessa  prorsa  is  the  summer  form, 
Vanessa  levana  the  winter  form  of  the  same  species. 
By  keeping  the  pupas  of  Vanessa  prorsa  several 
weeks  at  a  temperature  of  from  0°  to  1°  Weismann 
succeeded  in  obtaining  from  the  summer  chrysalids 
specimens  which  resembled  the  winter  variety,  Vanessa 
levana. 

If  we  wish  to  get  a  clear  understanding  of  the  causes 
of  variation  in  the  colour  and  pattern  of  butterflies, 
we  must  direct  our  attention  to  the  experiments  of 
Fischer,  who  worked  with  more  extreme  temperatures 
than  his  predecessors,  and  found  that  almost  identical 
aberrations  of  colour  could  be  produced  by  both  ex- 
tremely high  and  extremely  low  temperatures.  This  can 
be  seen  clearly  from  the  following  tabulated  results  of 
his  observations.  At  the  head  of  each  column  the 
reader  finds  the  temperature  to  which  Fischer  sub- 
mitted the  pupse,  and  in  the  vertical  column  below  are 
found  the  varieties  that  were  produced.  In  the  vertical 
column  A  are  given  the  normal  forms: 


304        The  Influence  of  Environment 

TABLE  XV 


o°  to 

o°  to 

A 

+35°  to 

+36°  to 

+42°  to 

-20°C. 

+  io°C. 

(Normal 
Forms) 

+2,7°  C. 

+4i°C. 

+46°C. 

ich:usoidcs 

Polaris 

iirticcB 

iclmusa 

Polaris 

ichnusoides 

(nigrita) 

(nigrita) 

antigone 

fischeri 

to 

— 

fischeri 

antigone 

{iokaste) 

(iokaste) 

testudo 

dixeyi 

polychloros 

erythromelas 

dixeyi 

testudo 

hygicEa 

artemis 

antiopa 

epione 

artemis 

hygicea 

elymi 

wiskotli 

cardui 

— 

luiskotli 

elymi 

klymene 

merrifieldi 

atalanta 

— 

merrifieldi 

klymene 

weismanni 

porima 

prorsa 

~ 

porima 

weismanni 

The  reader  will  notice  that  the  aberrations  produced 
at  a  very  low  temperature  (from  0°  to  —20°  C.)  are 
absolutely  identical  with  the  aberrations  produced  by 
exposing  the  pupce  to  extremely  high  temperatures 
(42°  to  46°  C).  Moreover,  the  aberrations  produced 
by  a  moderately  low  temperature  (from  0°  to  10°  C.) 
are  identical  with  the  aberrations  produced  by  a  moder- 
ately high  temperature  (36°  to  41°  C). 

From  these  observations  Fischer  concludes  that  it  is 
erroneous  to  speak  of  a  specific  effect  of  high  and  of 
low  temperatures,  but  that  there  must  be  a  common 
cause  for  the  aberration  found  at  the  high  as  well  as 
at  the  low  temperature  limits.  This  cause  he  seems 
to  find  in  the  inhibiting  effects  of  extreme  temperatures 
upon  development. 

If  we  try  to  analyse  such  results  as  Fischer's  from  a 


The  Influence  of  Environment 


0^0 


physicochemical  point  of  view,  we  must  realize  that 
what  w^e  call  life  consists  of  a  series  of  chemical  reac- 
tions, which  are  connected  in  a  catenary  way;  inas- 
much as  one  reaction  or  group  of  reactions  (a)  {e.  g., 
hydrolyses)  causes  or  furnishes  the  material  for  a 
second  reaction  or  group  of  reactions  (b)  (e.  g.,  oxida- 
tions). We  know  that  the  temperature  coefficient  for 
physiological  processes  varies  sHghtly  at  various  parts 
of  the  scale;  as  a  rule  it  is  higher  near  o°  and  lower  near 
30°.  But  we  know  also  that  the  temperature  coefficients 
do  not  vary  equally  for  the  various  physiological  pro- 
cesses. It  is,  therefore,  to  be  expected  that  the  tem- 
perature coefficients  for  the  group  of  reactions  of  the 
type  (a)  will  not  be  identical  through  the  whole  scale 
with  the  temperature  coefficients  for  the  reactions  of 
the  type  (b).  If  therefore  a  certain  substance  is  formed 
at  the  normal  temperature  of  the  animal  in  such  quan- 
tities as  are  needed  for  the  catenary  reaction  (b),  it  is 
not  to  be  expected  that  this  same  perfect  balance  will 
be  maintained  for  extremely  high  or  extremely  low 
temperatures;  it  is  more  probable  that  one  group  of 
reactions  will  exceed  the  other  and  thus  produce  aber- 
rant chemical  effects,  which  may  underHe  the  colour 
aberrations  observed  by  Fischer  and  other  experi- 
menters. 

It  is  important  to  notice  that  Fischer  was  also  able 
to  produce  aberrations  through  thc'  application  of 
narcotics.     Wolfgang    Ostw^ald   has   produced    experi- 


3o6        The  Influence  of  Environment 

mentally,  through  variation  of  temperature,  dimor- 
phism of  form  in  Daphnia. 

5.  Next  or  equal  in  importance  with  the  tempera- 
ture is  the  nature  of  the  mediimi  in  which  the  cells 
are  living. 

It  has  often  been  pointed  out  that  the  marine  animals 
and  the  cells  of  the  body  of  metazoic  animals  are 
surrounded  by  a  medium  of  similar  constitution,  the 
sea  water  and  the  blood  or  lymph,  both  media  be- 
ing salt  solutions  differing  in  concentration  but  con- 
taining the  three  salts  NaCl,  KCl,  and  CaCla  in  about 
the  same  relative  concentration,  namely  100  mole- 
cules NaCl  :  2.2  molecules  of  KCl  :  1.5  molecules  of 
CaClj.  This  has  suggested  to  some  authors  the  poetical 
dream  that  our  home  was  once  the  ocean,  but  we  can- 
not test  the  idea  since  imfortunately  we  cannot  experi- 
ment with  the  past.  Plants,  unicellular  fresh-water 
algas,  and  bacteria  do  not  demand  such  a  medium  for 
their  existence. 

Herbst  had  shown  that  when  sea-urchin  larvas  were 
raised  in  a  medium  in  which  only  one  of  the  constitu- 
ents of  the  sea  water  was  lacking  (not  only  NaCl,  KCl, 
or  CaCl,,  but  also  Na.SO^,  NaHC03,  or  Na.HPOJ, 
the  eggs  could  not  develop  into  plutei;  from  which  he 
concluded  that  every  constituent  of  the  sea  water  was 
necessary.  This  would  indicate  a  case  of  extreme 
adaptation  to  all  the  minutiae  of  the  external  medium. 

Experiments  on   a  much  more  favourable  animal 


The  Influence  of  Environment        307 

for  this  pinpose,  namely,  the  eggs  of  the  marine  fish 
Fimdulus,  gave  altogether  different  results.  The  eggs 
of  this  marine  fish  develop  naturally  in  sea  water  but 
they  develop  just  as  well  in  fresh  or  in  distilled  water, 
and  the  young  fish  when  they  are  made  to  hatch  in 
distilled  water  will  continue  to  live  in  this  medium. 
This  proves  that  these  eggs  require  none  of  the  salts 
of  the  sea  water  for  their  development.  When  these 
eggs  are  put  immediately  after  fertilization  into  a  pure 
solution  of  NaCl  of  that  concentration  in  which  this 
salt  exists  in  the  sea  water  practically  all  the  eggs  die 
without  forming  an  embryo;  but  if  a  small  quantity 
of  CaClz  is  added  every  egg  is  able  to  form  one, 
and  these  embryos  will  develop  into  fish  and  the  latter 
will  hatch.  This  led  the  writer  to  the  conclusion  that 
these  fish  (and  perhaps  marine  animals  in  general) 
need  the  Ca  of  the  sea  water  only  to  counteract  the 
injurious  effects  which  a  pure  XaCl  solution  has  if  it 
is  present  in  too  high  a  concentration.  ^  When  we  raise 
the  eggs  in  a  pure  NaCl  solution  of  a  concentration 
^m/8  practically  every  egg  will  develop;  and  even  in 
a  m/4  or  3/8  m  many  or  some  eggs  will  form  embryos 
without  adding  Ca ;  it  may  be  that  a  trace  of  Ca  present 
in  the  membrane  of  the  egg  may  suffice  to  counter- 
balance the  injurious  action  of  a  weak  salt  solution. 

'  Loeb,  J.,  "The  Poisonous  Character  of  a  Pure  XaCl  Solution," 
Am.  Jour.  Physiol.,  1900,  iii.,  S29;Arch.f.  d.  ges.  Physiol.,  1901,  Ixxxviii., 
68;  Am.  Jour.  Physiol.,  1902,  vi.,  411;  Biochem.  Ztschr.,  1906,  ii.,  8l. 


3o8       The  Influence  of  Environment 

The  concentration  of  the  NaCl  in  the  sea  water  at 
Woods  Hole  (where  these  experiments  were  made) 
is  about  m/2,  and  as  soon  as  this  concentration  of  NaCl 
is  reached  the  eggs  are  all  killed  as  a  rule  before  they 
can  form  an  embryo,  unless  a  small  but  definite  amount 
of  Ca  is  added.  It  was  found  that  the  eggs  can  be 
raised  in  much  higher  concentrations  of  NaCl,  but  in 
that  case  more  Ca  must  be  added.  The  following 
table  gives  the  minimal  amount  of  CaCU  which  must 
be  added  in  order  to  allow  fifty  per  cent,  of  the  eggs 
to  form  embryos.  (The  eggs  were  put  into  the  solu- 
tion an  hour  or  two  after  fertilization.) 

TABLE  XVI 


Concentration 

Cc.  ml  16  CaClz 

of 

Required  for  50  cc. 

NaCl 

NaCl  Solution 

m. 

3/8 

O.I 

4/8 

0.3 

5/8 

0.5 

6/8 

0.6 

7/8 

0.9 

8/8 

1.2-1.4 

9/8 

1.8-2.0 

10/8 

2.0-2.5 

11/8 

2.0? 

12/8 

3-0-3-5 

13/8 

6.0 

This  indicates  that  the  quantity  of  CaCU  required 
to  coimteract  the  injurious  effects  of  a  pure  solution 
of  NaCl  increases  approximately  in  proportion  to  the 


The  Influence  of  Environment        309 

square  of  the  concentration  of  the  NaCl  solution.'^ 
The  reader  will  notice  that  the  eggs  can  survive  and 
develop  in  a  solution  of  three  times  the  concentration 
of  sea  water,  provided  enough  Ca  is  added. 

It  was  found  also  that  not  only  Ca  but  a  large  num- 
ber of  other  bivalent  metals  were  able  to  counteract 
the  injurious  action  of  an  excessive  NaCl  solution; 
namely  Mg,  Sr,  Ba,  I\In,  Co,  Zn,  Pb,  and  Fe;^  only  Hg 
and  Cu  could  not  be  used  since  they  are  themselves 
too  toxic.  The  antagonistic  efficiency  of  the  bivalent 
cations  other  than  Ca  was,  however,  smaller  than 
that  of  Ca.  The  following  table  gives  the  high- 
est concentration  of  NaCl  solution  in  w^hich  the 
newly  fertilized  eggs  of  Fundulus  can  still  form  an 
embryo.  3 

50  CO.  10/8  m  NaCH-4  CO.  m/i  MgCU 
50  CO.  14/8  m  NaCl  + 1  c.c.  m/i  CaCU 
50  c.c.  1 1/8  m  NaCl  +  i  c.c.  m/i  SrCU 
50  c.c.    7/8  m  NaCH-i  c.c.  m/i  BaCU 

On  the  other  hand  it  was  seen  that  in  all  the  chlorides 
with  a  univalent  cation,  LiCl,  KCl,  RbCl,  CsCl, 
NH4CI,  the  eggs  could  form  embryos  up  to  a  certain 
concentration  of  the  salt ;  but  that  this  concentration 
could  be  raised  by  the  addition  of  Ca. 

^  Loeb,  J.,  Jour.  Biol.  Chem.,  1915,  xxiii.,  423. 

^  Loeb,  J.,  "On  the  Physiological  Effects  of  the  Valency  and  Possibly 
the  Electrical  Charges  of  Ions,"  Am.  Jour.  Physiol.,  1902,  vi.,  411. 
3  Loeb,  J.,  Jour.  Biol.  Chem.,  1914,  xix.,  431. 


310        The  Influence  of  Environment 


TABLE  XVII 

Concentrations  at  which  the  Eggs  no  longer  Are  Able  to 
Form  Embryos 


In  the  Pure  Salts 


In  the  Same  Salts  with  the  Addition 

of  I  ex.  m  CaCli  to  50  c.c. 

Solution 


LiCl about    6/32  m 

NaCl m/2 

KCl >ii/i6m 

<6/8m 
RbCl >8/8m 

<7/8m 
CsCl >3/8m 

<4/8  m 


>5/8ni 
>i4/8  m 
>   8/8  m 

>9/8m 

>8/8m 


In  short  it  turned  out  that  the  injurious  action  of 
the  pure  solution  of  any  chloride  (or  any  other  anion) 
with  a  univalent  metal  could  be  counteracted  to  a 
considerable  extent  by  the  addition  of  small  quantities 
of  a  salt  with  a  bivalent  metal.  It  was  also  found 
in  the  early  experiments  of  the  writer  that  the  bivalent 
or  polyvalefit  anions  had  no  such  antagonistic  effect  upon 
the  injurious  action  of  the  salts  with  a  univalent  cation. 

We  therefore  see  that  what  at  first  sight  appeared  in 
the  experiments  of  Herbst  a  necessity,  namely,  the 
presence  of  each  constituent  of  the  sea  water,  turns 
out  as  a  special  case  of  a  more  general  law;  the  salts 
with  univalent  ions  are  injurious  if  their  concentration 
exceeds  a  certain  hmit  and  this  injurious  action  is 
diminished  by  a  trace  of  a  salt  with  a  bivalent  cation. 

Why  was  it  not  possible  to  prove  this  fact  for  the 


The  Influence  of  Environment        311 

eggs  of  the  sea  urchin?  Before  we  answer  this  ques- 
tion, we  wish  to  enter  upon  the  discussion  of  the  nature 
of  the  injurious  action  of  a  pure  NaCl  solution  of  a 
certain  concentration  and  of  the  annihilation  of  this 
action  by  the  addition  of  a  small  quantity  of  Ca.  The 
writer  suggested  in  1905  that  the  injurious  action  of  a 
pure  NaCl  solution  consisted  in  rendering  the  membrane 
of  the  egg  permeable  for  NaCl,  whereby  the  germ 
inside  the  membrane  is  killed;  while  the  addition  of  a 
small  amount  of  Ca  (or  any  other  bivalent  metal) 
prevents  the  diffusion  of  Na  into  the  egg,  ^  possibly,  as 
T.  B.  Robertson^  suggested,  by  forming  a  precipitate 
with  some  constituent  of  the  membrane,  whereby  the 
latter  becomes  more  impermeable.  The  correctness 
of  this  idea  can  be  demonstrated  in  the  following  way. 
When  eggs  of  Fundulus,  which  are  three  or  four  days 
old  and  contain  an  embryo,  are  put  into  a  test-tube 
containing  3  m  NaCl  they  will  float  on  this  solution  for 
about  three  or  four  hours ;  after  that  they  will  sink  to 
the  bottom.  Before  this  happens  the  egg  will  shrink 
and  when  it  ceases  to  float  the  embryo  is  usually  dead. 
This  is  intelligible  on  the  assumption  that  the  NaCl 
solution  entered  the  egg,  increased  its  specific  gravity 
so  that  it  could  not  float  any  longer  and  killed  the 
embryo.  When  we  add,  however,  i  c.  c,  10/8  m 
CaCla  to  50  c.c.  3  m  NaCl  the  eggs  will  float,  the 

'  Loeb,  J.,  Arch.  f.  d.  ges.  Physiol.,  1905,  cvii.,  252. 
*  Robertson,  T.  B.,  Ergeb.  d.  Physiol.,  1910,  x.,  216. 


312        The  Influence  of  Environment 

heart  will  continue  to  beat  normally  and  the  em- 
bryo will  continue  to  develop  for  three  days  or  more, 
because  the  calcium  prevents  the  NaCl  from  entering 
into  the  egg.^  For  if  we  put  a  newly  hatched  embryo 
into  50  c.c.  3  m  NaCl+i  c.c.  10/8  m  CaCU  it  will  die 
almost  instantly;  hence  the  membrane  must  have 
acted  for  three  or  more  days  as  a  shield  which  pre- 
vented the  NaCl  from  diffusing  into  the  egg  in  the 
presence  of  CaCU. 

The  same  experiments  cannot  be  demonstrated  in 
the  sea-urchin  egg,  first,  because  it  can  live  neither  in 
distilled  water  nor  in  very  dilute  nor  very  concentrated 
solutions;  and  second,  because  it  is  not  separated  as  is 
the  germ  of  the  Fundulus  egg  from  the  surrounding 
solution  by  a  membrane  which  is  under  proper  condi- 
tions practically  impermeable  for  water  and  salts. 

Nevertheless  it  can  be  shown  that  the  results  at 
which  we  arrived  in  our  experiments  on  Fundulus 
are  of  a  general  application.  Osterhout^  has  shown 
that  plants  which  grow  in  the  soil  or  in  fresh  water 
are  readily  killed  by  a  pure  NaCl  solution  of  a  certain 
concentration,  while  they  can  resist  the  same  concen- 
tration of  NaCl  if  some  CaCU  is  added.  Wo.  Ostwald^ 
has  shown  the  same  for  a  species  of  Daphnia.  "We, 
therefore,  come  to   the  conclusion   that  the  injurious 

'  Loeb,  J.,  Biochem.  Zlschr.,  1912,  xlvii.,  127. 

'Osterhout,  W.  J.  V.,  Bot.  Gazette,  1906,  xlii.,  127;  1907,  xliv.,  257; 
Jour.  Biol.,  Ghent.,  1906,  i.,  363. 

J  Ostwald,  Wo.,  Arch.  f.  d.  ges.  Physiol.,  1905,  cvi.,  568. 


The  Influence  of  Environment        313 

action  following  an  alteration  in  the  constitution  of  the 
sea  water  is  in  some  of  the  cases  due  to  an  increase  in 
the  permeability  of  the  membranes  of  the  cell,  whereby 
substances  can  diffuse  into  the  cell  which  when  the 
proper  balance  prevails  cannot  diffuse.  For  this 
balance  the  ratio  of  the  concentration  of  the  salts  with 
univalent  cation  Na  and  K  over  those  with  bivalent 

^Na+K  salts 

cation  Ca  and  Me    -^ is  of  the  greatest 

CCa+Mg  salts 

importance. 

6.  The  importance  of  this  quotient  appears  in 
the  so-called  "behaviour"  of  marine  animals.  We 
have  mentioned  the  newly  hatched  larvae  of  the 
barnacle  in  connection  with  heliotropism.  These  larvs 
swim  in  a  trough  of  normal  sea  water  at  the  surface, 
being  either  strongly  positively  or  negatively  helio- 
tropic.  They  collect  as  a  rule  in  two  dense  clusters, 
one  at  the  window  and  one  at  the  room  side  of  the 
dish.  If  such  animals  are  put  into  a  solution  of  NaClH- 
KCl  (in  the  proportion  in  which  these  salts  exist  in 
the  sea  v/ater),  they  will  fall  to  the  bottom  unable  to 
rise  to  the  surface.  They  will,  however,  rise  to  the 
surface  and  swim  energetically  to  or  from  the  window 
if  a  certain  quantity  of  any  of  the  chlorides  of  a  biva- 
lent metal,  Mg,  Ca,  or  Sr,  is  added,  but  these  movements 
will  last  only  a  few  minutes  when  only  one  of  these 
three  salts  is  added;  and  then  the  animals  will  faU  to 
the  bottom  again.     If,  however,  two  salts,  e.  g.,  MgCU 


314        The  Influence  of  Environment 


and  CaClj,  are  added  the  animals  will  stay  permanently 
at  the  surface  and  react  to  light  as  they  would  have 
done  in  normal  sea  water.  These  animals  also  can 
resist  comparatively  large  changes  in  the  concentration 
of  the  sea  water,  and  it  seemed  of  interest  to  find  out 

u  .u       ,u  .'     .      CNaCl+KCl 

whether    the    quotient    Cm  CI  +CaCl  '  ^^^^^    ^^^^ 

allowed  all  the  animals  to  swim  at  the  surface,  had 
a  constant  value.  The  MgCU+CaCla  solution  was 
3/8  m  and  contained  the  two  metals  in  the  proportion 
in  which  they  exist  in  the  sea  water;  namely,  11.8  mole- 
cules MgCU  to  1.5  molecules  CaCU.  The  next  table 
gives  the  result.*  Since  these  experiments  lasted  a 
day  or  more  each,  usually  two  different  concentrations 
of  NaCl+KCl  of  the  ratio  1:2  or  1:4  were  compared 
in  one  experiment. 

TABLE  XVIII 


Number 

< 
Experiment 

Concentration 

of 
NaCl+KCl 

C.C.     ■  - 
3/8  m  CaCh-{- 
MgCh 
Required 

Value  of 
CNa+K 

CMg  +  Ca 

I 
2 
3 

j  m/i6  ' 
|m/8 

jm/8 
1  m/4 

j  3/16  m 
]3/8m 

0.3 
0.4-0.5 

0-5 
0.9-1.0 

0.7 
1-3 

27.8 
37-0 

33-3 
35-1 

357 
38.5 

'  Loeb,  J.,  Jour.  Biol.  Chem.,  1915,  xxiii.,  423. 


The  Influence  of  Environment        315 

TABLE  XVlll— Continued 


Number 
Experiment 

Concentration 

of 
NaCl+KCl 

C.C. 

j/8  m  CaCl2  + 

MgCh 

Required 

Value  of 
CNa+K 

CMg  +  Ca 

4 
5 
6 

7 

jm/8 
jm/2 

jm/2 

(  5/16  m 
]5/8m 

j  3/16  m 
■j  6/8  m 

0-5 
1. 8-1.9 

0.8-0.9 
1. 6-1. 7 

0.9 
1-7 

0.6 

2.4 

36.0 
39-2 

39-2 
40.3 

46.3 
49.0 

41.7 
41.7 

These  experiments  indicate  that  the  ratio  of  7;;^ 

^  Cca+A:g 

remains  very  neariy  constant  with  varying  concentra- 
tions of  CNa+K. 

In  former  experiments  on  jellyfish  the  writer  had 
shown  that  there  exists  an  antagonism  between  Mg 
and  Ca^,  and  this  observation  was  subsequently  con- 
firmed by  Meltzer  and  Auer^  for  mammals.  It  was 
observed  that  in  a  solution  of  NaCl+KCl+MgCU 
the  larvae  of  the  barnacle  were  also  not  able  to  remain 
at  the  surface  for  more  than  a  few  minutes,  while  an 
addition  of  some  CaCU  made  them  swim  permanently 
at  the  surface.  Various  quantities  of  MgCU  were 
added  to  a  mixture  of  m/4  or  m/2  NaC14-KCl,  to  find 

'  Loeb,  J.,  Jour.  Biol.  Chem.,  1905-06,  i.,  427. 

*  Meltzer,  S.  J.,  and  Auer,  J.,  Am.  Jour.  Physiol.,  1908,  xxi.,  400. 


3i6        The  Influence  of  Environment 

out  how  much  CaCU,  was  required  to  allow  them  to 
swim  permanently  at  the  surface. 
TABLE  XIX 


C.c.  of  ml  16 

CaCh  Neces- 

sary  to  Induce  the  Ma- 

jority   of   the    LarvcB    to 

Swim  in 

m/2(Na+K) 

m/4(Na+K) 

50  uc.  NaCl+KCl+0.75 

c.c.  3/8mMgCl2 

0.2 

50C.C.  NaCl+KCl+  1.5 

c.c.  3/8  m  MgCb 

0.4 

0.3 

50C.C.  NaCl+KCH-  2.5 

c.c.  3/8  m  MgCb 

0.4 

0.4 

50C.C.  NaCl+KCl+  5.0 

c.c.  3/8  m  MgCh 

0.7-0.8 

0.7-0.8 

50  c.c.  NaCl+KCl  +  io.o 

c.c.  3/8  m  MgCh 

1.6 

1.6 

50C.C.  NaCl+KCl  +  15.0 

c.c.  3/8  m  MgCla 

1.8 

50C.C.  NaCl+KCl+20.0 

c.c.  3/8  m  MgClz 

1.8 

In  order  to  interpret  these  figures  correctly  we  must 
remember  that  we  are  dealing  with  two  different  an- 
tagonisms, one  between  the  salts  with  univalent  and 
bivalent  metals  and  the  other  between  Mg  and  Ca. 
The  former  antagonism  is  satisfied  by  the  addition  of 
Mg,  inasmuch  as  enough  Mg  was  present  for  this 
purpose  in  all  solutions.  What  was  lacking  was  the 
balance  between  Mg  and  Ca.  The  experiments  in 
Table  XIX  therefore  answer  the  question  of  the  ratio 
between  Mg  and  Ca.  If  we  consider  only  the  concen- 
trations of  Mg  between  2.5  and  lo.o  c.  c.  3^  m  MgCU 
— which  are  those  closest  to  the  normal  concentration 
of  Mg  in  the  sea  water — we  notice  that  CCa  must 
vary  in  proportion  to  CjVTg.  If  we  now  combine  the 
results  of  this  and  the  previous  paragraph  we  may 


The  Influence  of  Environment        317 

express  them  in  the  form  of  the  theory  of  physiologically 
balanced  salt  solutions,  by  which  we  mean  that  in  the  ocean 
{and  in  the  blood  or  lymph)  the  salts  exist  in  such  ratio 
that  they  mutually  antagonize  the  injurious  action  which 
one  or  several  of  them  would  have  if  they  were  alone  in 
solution,^  This  law  of  physiologically  balanced  solu- 
tions seems  to  be  the  general  expression  of  the  effect 
of  changes  in  the  constitution  of  the  salt  solutions  for 
marine  or  all  aquatic  organisms. 

This  chapter  would  not  be  complete  without  an 
intimation  of  the  role  of  buffers  in  the  sea  water  and 
the  blood,  by  which  the  reaction  of  these  media  is  pre- 
vented from  changing  in  a  way  injurious  to  the  organ- 
ism. These  buffers  are  the  carbonates  and  phosphates. 
Instead  of  saying  that  the  organisms  are  adapted  to 
the  medium,  L.  Henderson  has  pointed  out  the  fitness 
of  the ,  environment  for  the  development  of  organisms 
and  one  of  these  elements  of  fitness  are  the  buffers  against 
alterations  of  the  hydrogen  ion  concentration.^  The 
ratio  in  which  the  salts  of  the  different  metals  exist  in 
the  sea  water  is  another.  It  is  obvious  that  the  quan- 
titative laws  prevailing  in  the  effect  of  environment 
upon  organisms  leave  no  more  room  for  the  interfer- 
ence of  a  "directing  force"  of  the  vitalist  than  do  the 
laws  of  the  motion  of  the  solar  system. 

'  This  theory  was  first  expressed  by  the  writer  in  Am.  Jour.  Physiol., 
1900,  iii.,  434. 

^Henderson,  L.,  The  Fitness  of  the  Environment.  See  also  Michaelis, 
L.,  Die  Wasserstoffionenconzentration.     Berlin,  1914. 


CHAPTER  XII 

ADAPTATION   TO  ENVIRONMENT 

I .  It  is  assumed  by  certain  biologists  that  the  envir- 
onment influences  the  organism  in  such  a  way  as  to 
increase  its  adaptation.  Were  this  correct  it  would 
not  contradict  a  purely  physicochemical  conception  of 
life ;  it  would  only  call  for  an  explanation  of  the  me- 
chanism by  which  the  adaptation  is  brought  about. 
There  are  striking  cases  on  record  which  warn  us 
against  the  universal  correctness  of  the  view  that 
the  environment  causes  an  adaptive  modification  of 
the  organism.  Thus  the  writer  pointed  out  in  1889 
that  positive  heliotropism  occurs  in  organisms  which 
have  no  opportunity  to  make  use  of  it,*  e.  g.,  Cuma 
rathkii,  a  crustacean  living  in  the  mud,  and  the 
caterpillars  of  the  willow  borer  living  under  the  bark 
of  the  trees.  We  understand  today  why  this  should 
be  so,  since  heliotropism  depends  upon  the  presence  of 
photosensitive  substances,  and  it  can  readily  be  seen 

'  Loeb,  J.,  Der  Heliotropismus  der  Tiere  und  seine  Ubereinstimmung 
mil  dem  Heliotropismus  der  Pflanzen.  Wurzburg,  1890  (appeared  in 
1889). 

318 


Adaptation  to  Environment  319 

that  the  question  of  use  or  disuse  has  nothing  to  do 
with  the  production  of  certain  harmless  chemical  com- 
pounds in  the  body.  A  much  more  striking  example 
is  offered  in  the  case  of  galvanotropism.  !Many  or- 
ganisms show  the  phenomenon  of  galvanotropism, 
yet,  as  the  writer  pointed  out  years  ago,  galvano- 
tropism is  purely  a  laborator}^  product  and  no  animal 
has  ever  had  a  chance  or  will  ever  have  a  chance  to 
be  exposed  to  a  constant  current  except  in  the  labora- 
tor}"  of  a  scientist.  This  fact  is  as  much  of  a  puzzle 
to  the  selectionist  and  to  the  Lamarckian  (who  would 
be  at  a  loss  to  explain  how  outside  conditions  could 
have  developed  this  tropism)  as  to  the  vitaHst  who 
would  have  to  admit  that  the  genes  and  supergenes 
indulge  occasionally  in  queer  freaks  and  lapses.  The 
only  consistent  attitude  is  that  of  the  ph^^sicist  who 
assumes  that  the  reactions  and  structures  of  animals 
are  consequences  of  the  chemical  and  physical  forces, 
which  no  more  ser\'e  a  purpose  than  those  forces  re- 
sponsible for  the  solar  systems.  From  this  viewpoint 
it  is  comprehensible  why  utterly  useless  tropisms  or 
structures  should  occur  in  organisms. 

2.  A  famous  case  for  the  apparent  adaptation  of 
animals  to  environment  has  been  the  bhnd  cave  ani- 
mals. It  is  known  that  in  caves  bhnd  salamanders, 
blind  fishes,  and  blind  insects  are  common,  while  such 
forms  are  comparatively  rare  in  the  open.  This  fact 
has  suggested  the  idea  that  the  darkness  of  the  cave 


320  Adaptation  to  Environment 

was  the  cause  of  the  degeneration  of  the  eyes.  A  closer 
investigation  leads,  however,  to  a  different  explanation. 
Eigenmann  has  shown  that  of  the  species  of  salamanders 
Hving  habitually  in  North  American  caves,  two  have 
apparently  quite  normal  eyes.  They  are  Spelerpes 
maculicaiida  and  Spelerpes  stejnegeri.  Two  others  liv- 
ing in  caves  have  quite  degenerate  eyes,  Typhlotriton 
spelcBus  and  Typhlomolge  rathbuni.  If  disuse  is  the 
direct  cause  of  blindness  we  must  inquire  why  Spelerpes 
is  not  blind. 

Another  difficulty  arises  from  the  fact  that  a  blind 
fish  TyphlogohiiLS  is  found  in  the  open  (on  the  coast  of 
southern  California)  in  shallow  water,  where  it  lives 
under  rocks  in  holes  occupied  by  shrimps.  The 
question  must  again  be  raised:  How  can  it  happen 
that  in  spite  of  exposure  to  light  Typhlogobius  is 
blind? 

The  most  important  fact  is  perhaps  the  one  found 
by  Eigenmann  in  the  fishes  of  the  family  of  Amblyop- 
sidas.  Six  species  of  this  group  live  permanently  in 
caves,  are  not  found  in  the  open,  and  have  abnormal 
eyes,  while  one  lives  permanently  in  the  open,  is  never 
found  in  caves,  and  one  comes  from  subterranean 
springs.  The  one  form  which  is  found  only  in  the 
open,  Chologaster  cornutus,  has  a  simplified  retina  as 
well  as  a  comparatively  small  eye,  in  other  words,  its 
eye  is  not  normal.  This  indicates  the  possibihty  that 
the   other   representatives   which   are   found   only   in 


Adaptation  to  Environment  321 

caves  also  might  have  abnormal  eyes  even  if  they  had 
never  lived  in  caves. 

Through  these  facts  the  old  idea  becomes  question- 
able, namely,  that  the-  cave  animals  had  originally 
been  animals  with  normal  eyes  which  owing  to  disuse 
had  undergone  a  gradual  hereditary  degeneration. 

Recent  experiments  made  on  the  embryos  of  the  fish 
Ftuididus  have  yielded  the  result  that  it  is  possible  to 
produce  blindness  in  fish  by  various  means  other  than 
lack  of  light.  ^  Thus  the  writer  found  that  by  crossing 
the  egg  of  Fundulus  with  the  sperm  of  a  widely  different 
species,  namely,  Menidia,  blind  embryos  were  produced 
very  frequently;  that  is  to  say  such  embryos  had  the 
degenerate  eyes  characteristic  of  blind  cave  fishes. 
Very  often  no  other  external  trace  of  an  eye,  except  a 
gathering  of  pigment,  could  be  found,  while  a  close 
histological  examination  would  possibly  have  resulted 
in  the  demonstration  of  rudiments  of  a  lens  and  other 
tissues  of  the  eye. 

Another  method  of  producing  blind  fish  embryos 
consists  in  exposing  the  egg  immediately,  or  soon  after 
fertilization,  to  a  temperature  between  0°  and  2°  C. 
for  a  number  of  hours.  Many  embryos  are  killed  by 
this  treatment,  but  those  which  survive  behave  very 
much  like  the  hybrids  between  Fundulus  and  Menidia, 
i.  e.,  a  number  of  them  have  quite  degenerated  eyes. 
If  the  eggs  have  once  formed  an  embryo  they  can  be 

\Loeb,  J.,  Biol.  Bull,  1915,  xxix.,  50. 

21 


322  Adaptation  to  Environment 

kept  at  the  temperature  of  o°  for  a  month  or  more 
without  giving  rise  to  bUnd  animals.  Occasionally 
such  rudimentary  eyes  were  also  observ^ed  when  eggs 
were  kept  in  a  solution  containing  a  trace  of  KCN. 
Stockard  has  succeeded  in  producing  cyclopean  eyes 
in  Fiindulus  by  adding  an  excess  of  magnesium  salt 
to  the  sea  water  in  which  the  eggs  developed  or  by 
adding  alcohol,  and  McClendon  has  confirmed  and 
added  to  these  results. 

The  writer  tried  repeatedly,  but  in  vain,  to  produce 
Fundulus  with  deficient  eyes  by  keeping  the  embryos 
in  the  dark.  Sperm  and  egg  were  not  allowed  to  be 
exposed  to  the  light  yet  the  embryos  without  exception 
had  normal  eyes. 

F.  Payne  raised  sixty-nine  successive  generations  of 
a  fly  Drosophila  in  the  dark,  but  the  eyes  and  the  re- 
action of  the  insects  to  light  remained  perfectly  normal. 

Uhlenhuth  has  recently  demonstrated  in  a  very 
striking  way  that  the  development  of  the  eyes  does 
not  depend  upon  the  influence  of  light  or  upon  the 
eyes  functioning.  He  transplanted  the  eyes  of  young 
salamanders  into  different  parts  of  their  bodies  where 
they  were  no  longer  connected  with  the  optic  nerves. 
The  eyes  after  transplantation  underwent  a  degenera- 
tion which  was  followed  by  a  complete  regeneration. 
He  showed  that  this  regeneration  took  place  in  com- 
plete darkness  and  that  the  transplanted  eyes  remained 
normal  in   salamanders  kept  in   the   dark  for  fifteen 


Adaptation  to  Environment  323 

months.  Hence  the  eyes  which  were  no  longer  in 
connection  with  the  central  nervous  system,  which 
had  received  no  light,  and  could  not  have  functioned, 
regenerated  and  remained  normal.  The  degeneration 
which  took  place  in  the  eyes  immediately  after  being 
transplanted  was  apparently  due  to  the  interruption 
of  the  circulation  in  the  eye,  and  the  regeneration 
commenced  in  all  probability  with  the  re-estabhshment 
of  the  circulation  in  the  transplanted  organ. 

In  our  own  experiments  it  can  be  shown  that  the 
circulation  in  the  embryo  was  deficient  in  all  cases 
where  the  eyes  degenerated.  The  hybrids  between 
Fundulus  and  Menidia  have  often  a  beating  heart  but 
rarely  a  circulation  (although  they  form  blood) ;  and 
the  same  phenomenon  occurred  in  the  embryos  which 
were  exposed  to  a  low  temperature  at  an  early  period 
of  their  lives.  Hence  all  the  facts  agree  that  conditions 
which  lead  to  an  abnormal  circulation  (and  conse- 
quently also  to  an  abnormal  or  inadequate  nutrition 
of  the  embryonic  eye)  may  prevent  development  and 
lead  to  the  formation  of  bhnd  fishes.  Eigenmann 
states  that  no  blood-vessels  enter  the  eye  of  the  blind 
cave  salamander  Typhlotriton.  The  presence  or  ab- 
sence of  light  does  not  usually  interfere  with  the  circu- 
lation or  nutrition  of  the  embryonic  eye,  and  hence 
does  not  as  a  rule  lead  to  the  formation  of  degenerated 
eyes. 

This  would  lead  us  to  the  assumption  that  the  blind 


324  Adaptation  to  Environment 

fish  owe  their  deficiency  not  to  lack  of  hght  but  to  a 
condition  which  interferes  with  the  circulation  in  the 
embryonic  eye.  Such  a  condition  might  be  brought 
about  by  an  anomaly  in  the  germ  plasm  or  in  one 
chromosome,  the  nature  and  cause  of  which  we  are  not 
able  to  determine  at  present ;  but  which,  since  it  occurs 
in  the  germ  plasm  or  the  chromosomes,  must  be  heredi- 
tary. This  would  explain  why  it  is,  that  animals 
with  perfect  eyes  may  occur  in  caves  and  why  perfectly 
blind  animals  may  occur  in  the  open.  It  leaves,  how- 
ever, one  point  unexplained;  namely,  the  greater  fre- 
quency of  blind  species  in  caves  or  in  the  dark  and  the 
relative  scarcity  of  such  forms  in  the  open. 

Eigenmann  has  shown  that  all  those  forms  which 
live  in  caves  were  adapted  to  life  in  the  dark  before 
they  entered  the  cave.^  These  animals  are  all  nega- 
tively heliotropic  and  positively  stereotropic,  and  with 
these  tropisms  they  would  be  forced  to  enter  a  cave 
whenever  they  are  put  at  the  entrance.  Even  those 
among  the  Amblyopsidee  which  live  in  the  open  have 
the  tropisms  of  the  cave  dweller.  This  eliminates  the 
idea  that  the  cave  adapted  the  animals  for  the  life  in 
the  dark. 

Only  those  animals  can  thrive  in  caves  which  for  their 
feeding  and  mating  do  not  depend  upon  visual  mechan- 

*  Cu6not  has  proposed  the  term  preadaptation  for  such  cases  and 
this  term  expresses  the  situation  correctly.  Cu^not,  L.,  La  Cenese  des 
Especes  animales.     Paris,  191 1, 


Adaptation  to  Environment  325 

isms;  and  conversely,  animals  which  are  not  provided 
with  visual  mechanisms  can  hold  their  own  in  the  open, 
where  they  meet  the  competition  of  animals  which 
can  see,  only  under  exceptional  conditions.  This  seems 
to  account  for  the  fact  that  in  caves  blind  species  are 
comparatively  more  prevalent  than  in  the  open. 

In  other  words,  the  adaptation  of  blind  animals  to 
the  cave  is  only  apparent;  they  were  adapted  to  cave 
life  before  they  entered  the  cave.  Many  animals  are 
obviously  bxurdened  with  a  germinal  abnormality 
giving  rise  to  imperfection  and  smallness  of  the  eye — 
the  hereditary  factor  involved  may  have  to  do  with 
the  development  of  the  blood-vessels  and  lymphatics 
of  the  eye.  Such  mutants  can  survive  more  easily  in 
the  cave,  where  they  do  not  have  to  meet  the  competi- 
tion of  seeing  forms,  than  in  the  open.  In  man  also  an 
hereditary  form  of  blindness  is  known,  the  so-called 
hereditary  glaucoma.  It  has  nothing  to  do  with  light, 
but  the  disease  seems  to  be  due  to  an  hereditary 
anomaly  of  the  circulation  in  the  eye. 

Kammerer^  has  recently  reported  that  by  keeping 
the  blind  European  cave  salamander  Proteus  anguinus 
under  certain  conditions  of  illumination  he  succeeded 
in  producing  two  specimens  with  larger  eyes.  Accord- 
ing to  him  the  eyes  of  Proteus  may  develop  to  a 
certain  point  and  then  retrogress  again.  He  states 
that  by  keeping  young  salamanders  alternately  for  a 

*  Kammerer,  P.,  Arch.  f.  Entwcklngsmech.,  1912,  xxxiii.,  349. 


326  Adaptation  to  Environment 

week  or  two  in  sunlight  and  in  a  dark  room  where 
they  were  exposed  to  red  incandescent  hght,  two  males 
formed  somewhat  larger  eyes.  The  first  year  no  altera- 
tion was  visible.  In  the  second  year  a  slight  increase 
in  the  size  of  the  eyes  was  noticeable  under  the  skin. 
In  the  third  year  the  eye  protruded  slightly  and  this 
increased  somewhat  in  the  fourth  year. 

There  is  thus  far  only  one  case  on  record  in  animal 
biology  in  which  the  light  influences  the  formation  of 
organs.  The  writer  found  that  the  regeneration  of  the 
polyps  of  the  hydroid  Eudendrium  does  not  take  place 
if  the  animals  are  kept  in  the  dark,  while  the  polyps 
will  regenerate  if  exposed  to  the  light ;  ^  and  the  time  of 
exposure  may  be  rather  short  according  to  Goldfarb."* 
It  is  possible  that  Proteus  resembles  in  this  respect 
Eudendrium;  it  should  be  stated,  however,  that  of 
many  different  forms  tried  by  the  writer  over  a  number 
of  years,  Eudendrium  was  the  only  one  which  gave  evid- 
ence of  such  an  influence  of  light.  Of  course  it  is  not 
impossible  that  the  light  might  influence  reflexly  the 
development  of  blood-vessels  in  the  eyes  of  certain 
animals,  e.  g.,  Proteus,  and  thus  allow  the  eyes  of  Proteus 
to  grow  a  little  larger. 

We  therefore  come  to  the  conclusion  that  it  is  not 
the  cave  that  made  animals  blind  but  that  animals  with 
a  hereditary  tendency  towards  a  degeneration  of  the 

'  Loeb,  J.,  Arch.  d.  f.  ges.  Physiol.,  1896,  Ixiii.,  273. 

"  Goldfarb,  A.  J.,  Jour.  Exper.  ZooL,  1906,  iii.,  129;  1910,  viii.,  133. 


Adaptation  to  Environment  327 

eyes  can  survive  in  a  cave  while  they  can  only  excep- 
tionally survive  in  the  open.  The  cause  of  the  de- 
generation is  a  disturbance  in  the  circulation  and 
nutrition  of  the  eye,  which  is  as  a  rule  independent  of 
the  presence  or  absence  of  light. 

We  may  by  way  of  a  digression  stop  for  a  moment  to 
consider  the  most  astonishing  and  uncanny  case  of 
adaptation;  namely,  the  formation  of  the  transparent 
refractive  media,  especially  the  lens  in  front  of  the 
retina.  It  is  due  to  these  media  that  the  rays  which 
are  sent  out  by  a  luminous  point  can  be  united  to  an 
image  point  on  the  retina.  One  part  of  this  process  is 
understood ;  namely,  the  formation  of  a  lens.  Wherever 
the  optic  cup  of  the  embryo  is  transplanted  under  the 
epithelium  the  latter  will  be  transformed  into  a  trans- 
parent lens.  When  the  upper  edge  of  the  iris  is  in- 
jured in  the  salamander  so  that  the  cells  can  multiply, 
the  mass  of  newly  formed  cells  also  becomes  transparent 
and  a  lens  is  formed.  This  indicates  the  existence  of 
a  substance  in  the  optic  cup  which  makes  the  epithelial 
cells  transparent;  and  which  also  limits  the  size  of  the 
lens  which  is  formed.  The  lens  is  not  always  a  perfect 
optical  instrument,  on  the  contrary,  it  is  as  a  rule 
somewhat  defective.  Of  course,  a  great  many  details 
concerning  the  process  of  lens  regeneration  have  still 
to  be  worked  out. 

3.  It  is  well  known  that  most  marine  animals  die  if 
put  into  fresh  water  and  vice  versa;  and  in  salt  lakes  or 


328  Adaptation  to  Environment 

ponds  with  a  concentration  of  salt  so  high  that  most 
marine  animals  would  succumb  if  suddenly  transferred 
to  such  a  solution  we  have  a  limited  faima  and  flora. 
The  common  idea  is  that  marine  animals  become 
adapted  to  fresh  water  or  vice  versa;  or  to  the  condi- 
tions in  salt  lakes;  especially  if  the  changes  take  place 
gradually.  Yet  it  can  be  shown  that  the  existence  of 
these  different  faunas  can  be  explained  without  the 
assumption  of  an  adaptive  effect  of  the  environment. 
The  writer  has  worked  with  a  marine  fish  Fundulus 
whose  eggs  develop  naturally  in  sea  water  which,  how- 
ever, will  develop  just  as  well  in  distilled  water;  and 
the  young  fish  hatching  in  distilled  water  live  and  grow 
in  this  medium.  Most  of  the  adult  fish  die  after  several 
days,  when  put  suddenly  into  distilled  water,  but  they 
can  live  in  fresh  water  which  contains  only  a  trace  of 
salt.  They  can  also  live  in  very  concentrated  sea 
water,  e.  g.,  twice  the  normal  concentration.  Suppose 
that  a  bay  of  the  ocean  containing  such  fish  should 
suddenly  become  landlocked  and  the  concentration 
of  the  sea  water  be  thus  raised  to  twice  its  natural 
amount;  the  majority  of  forms  would  die  and  only 
Fundulus  and  possibly  a  few  other  species  with  the 
same  degree  of  resistance  would  survive.  An  investi- 
gator examining  the  salinity  of  the  water  and  not  know- 
ing the  natural  resistance  of  Fundulus  to  changes  in 
concentration  would  be  inclined  to  assume  that  he  had 
before  him  an  instance  of  a  gradual  adaptation  of  the 


Adaptation  to  Environment  329 

fish  to  a  higher  concentration  of  the  sea  water ;  whereas 
the  fish  was  already  immune  to  this  high  concentration 
before  coming  in  contact  with  it. 

This  fish  seemed  a  favourable  object  from  which  to 
find  out  how  far  an  adaptation  to  the  environment 
really  existed;  and  the  result  was  surprising.  By 
changing  the  concentration  of  the  sea  water  gradually 
it  is  possible  to  raise  the  natural  resistance  of  the  fish 
only  a  trifle,  not  much  over  ten  per  cent.  The  con- 
centration of  the  natural  sea  water  is  a  little  over  that 
of  a  m/2  solution  of  NaCl+KCl+CaCU  in  the  pro- 
portion in  which  these  three  salts  exist  in  the  sea  water. 
When  adult  Fundulus  are  put  into  a  10/8  m  solution 
of  NaCl-l-KCl+CaCU  in  the  proportion  in  which  these 
salts  occur  in  sea  water  they  die  in  less  than  a  day,  but 
when  put  from  sea  water  directly  into  a  8/8  m  or 
9/8  m  solution  they  can  five  indefinitely.  It  was  found  ^ 
that  if  the  concentration  of  the  sea  water  was  raised 
gradually  (by  m/8  a  day)  the  fish  on  the  fifth  day  could 
resist  a  10/8  m  solution  of  NaCl-f-KCl+CaCU  for  a 
month  (or  possibly  indefinitely;  the  experiment  was 
discontinued  after  that  period).  When  a  10/8  m  solu- 
tion was  allowed  to  become  more  concentrated  slowly 
by  evaporation  (at  room  temperature)  all  the  fish  died 
rapidly  when  the  concentration  was  12/8  m  or  even 
below.  In  higher  concentrations  they  can  live  only 
a  day  or  two.     These  experiments  show  that  while  the 

^  Loeb,  J.,  Biochem.  Ztschr.,  1913,  liii.,  391. 


330  Adaptation  to  Environment 

fish  is  naturally  immune  to  a  9/8  m  NaCl+KCl+CaCU 
solution,  by  the  method  of  slowly  raising  the  concen- 
tration it  may  be  made  to  tolerate  a  10/8  m  or  11/8  m 
solution,  but  not  more.  These  fish  when  once  adapted 
to  a  10/8  m  solution  can  be  put  suddenly  into  a  very 
weak  solution,  e.  g.,  a  m/80  NaCl,  without  suffering  and 
when  brought  back  into  a  10/8  m  solution  of  NaCl-}- 
KCl+CaCla  they  will  continue  to  live.  If  they  remain 
for  several  days  in  the  weak  solution  their  power  of 
resistance  to  10/8  m  NaCl+KCl+CaCU  solution  is 
weakened. 

What  change  takes  place  when  the  fish  is  made  more 
resistant  and  why  is  its  normal  resistance  so  great  .f* 
The  answer  based  on  the  writer's  experiments  seems 
to  be  as  follows:  Fundulus  is  comparatively  resistant 
to  sudden  changes  in  the  concentration  of  the  sea  water 
between  m/80  and  9/8  m  because  it  possesses  a  com- 
paratively impermeable  skin  whose  permeability  is 
not  seriously  altered  by  sudden  changes  within  these 
limits  of  concentration;  while  if  these  limits  are  ex- 
ceeded and  the  fish  are  brought  suddenly  into  too  high 
a  concentration  the  skin  becomes  permeable  and  the 
fish  dies,  the  gills  becoming  unfit  for  use  or  nerves 
being  injured  by  the  salt  which  diffuses  into  the  fish. 

The  fact,  that  by  slowly  raising  the  concentration 
to  10/8  m  the  fish  may  resist  this  limit,  is  in  reality 
no  adaptation.  There  is  no  sharp  limit  between  the 
injurious  and  non-injurious  concentration.     We  have 


Adaptation  to  Environment  331 

seen  that  the  fish  is  naturally  immune  to  a  9/8  m  solu- 
tion. It  is  also  naturally  immune  to  a  10/8  m  or  1 1/8  m 
solution  if  we  give  it  time  to  compensate  the  injurious 
effects  of  a  10/8  m  solution  by  the  repairing  action  of 
its  blood  or  kidneys.  Beyond  this  no  rise  is  possible. 
In  reality  adaptation  does  not  exist  in  this  case. 

In  former  experiments  the  writer  had  shown  that  a 
pure  NaCl  solution  of  that  concentration  in  which  this 
f.sh  naturally  lives  kills  it  very  rapidly,  while  it  lives 
in  such  a  solution  indefinitely  if  a  little  CaCU  is  added. 
The  explanation  of  this  fact  is  that  the  pure  NaCl  solu- 
tion is  able  to  diffuse  into  the  tissues  of  the  animal 
while  the  addition  of  a  trace  of  CaCU  renders  the  mem- 
brane practically  impermeable  to  NaCl.  The  question 
then  arose  whether  it  was  possible  to  make  the  fish  more 
resistant  to  a  pure  NaCl  solution  of  sufficiently  high 
concentration  and  how  this  could  be  done.  On  the  basis 
of  the  idea  of  an  adaptive  effect  of  the  environment  we 
should  expect  that  by  gradually  raising  the  concentra- 
tion of  a  pure  NaCl  solution  the  latter  would  gradually 
alter  the  animal  and  'make  it  more  resistant.  The 
method  of  procedure  suggested  was  therefore  to  put 
the  fish  first  in  low  and  gradually  into  increasing  con- 
centrations of  NaCl.  This  method  was  tried  and  found 
futile  for  the  purpose.  Fundulus  when  put  from  sea 
water  (after  having  been  washed)  into  a  6/8  m  NaCl 
solution  die  in  about  four  hours.  When  kept  previ- 
ously in  a  weaker  NaCl  solution  they  die  if  anything 


332  Adaptation  to  Environment 

more  quickly.  But  it  is  possible  to  make  them  live 
longer  in  a  6/8  m  solution  of  NaCl ;  we  have  to  proceed, 
however,  by  a  method  which  is  in  contrast  with  the 
ideas  of  the  adaptive  influence  of  the  environment. 
When  the  fish  are  first  treated  with  sea  water  (or  with 
a  mixture  of  NaCl+KCl+CaCU)  of  a  higher  concen- 
tration so  that  they  become  adapted  to  a  10/8  m  solu- 
tion of  NaCl+KCl+CaCU  or  to  10/8  m  sea  water, 
they  become  also  more  resistant  to  an  otherwise  toxic 
solution  of  NaCl.  Fish  taken  directly  from  sea  water 
were  killed  in  less  than  four  hours  when  put  into  a 
6/8  m  NaCl  solution,  while  fish  of  the  same  lot  previously 
adapted  to  10/8  m  sea  water  in  the  manner  described 
above  lived  two  or  three  days  in  a  6/8  m  NaCl  solution. ' 

It  is  not  impossible  that  it  was  the  high  concentration 
of  calcium  in  the  10/8  m  sea  water  which  rendered  the 
fish  more  immune  to  a  subsequent  treatment  with  NaCl. 
We  know  why  a  pure  NaCl  solution  kills  them  and  we 
also  know  why  the  addition  of  CaCla  protects  them 
against  this  pernicious  effect.  It  is  rather  strange  that 
where  the  conditions  of  the  experiments  are  clear  we 
find  nothing  to  indicate  an  adaptive  effect  of  the 
environment. 

4.  Ehrlich's  work  on  trypanosomes  seems  to  indicate 
a  remarkable  power  of  adaptation  on  the  part  of  or- 
ganisms to  certain  poisons.  If  the  writer  understands 
these  experiments  correctly  they  consisted  in  infecting 

'  Loeb,  J.,  Biochem.  Ztschr.,  1913,  liii.,  391. 


Adaptation  to  Environment  333 

a  mouse  with  a  certain  strain  of  trypanosomes,  and 
treating  it  with  a  certain  arsenic  compound,  which 
inhibited  somewhat  the  propagation  of  the  parasites 
but  did  not  kill  them  all.  Four  or  five  days  later 
trypanosomes  from  this  mouse  were  transmitted  to 
another  mouse  and  after  twenty-four  hours  this  mouse 
was  treated  with  a  stronger  dose  of  the  same  arsenic 
compound;  and  this  process  was  repeated.  After  the 
third  transmission  or  later,  the  trypanosomes  can  resist 
considerably  higher  doses  of  the  same  poison  than  at 
first  and  this  resistance  is  retained  for  years.  Ehrlich 
seems  to  have  taken  it  for  granted  that  he  had  succeeded 
in  transforming  the  surviving  trypanosomes  into  a 
type  which  is  permanently  more  resistant  to  the  arsenic 
compound  than  was  the  original  strain. 

The  writer  is  not  entirely  convinced  that  in  these 
experiments  a  possibility  was  sufficiently  considered 
which  is  suggested  by  Johannsen's  experiments  on  the 
importance  of  pure  lines  in  work  on  heredity.  Ac- 
cording to  this  author  a  strain  of  trypanosomes  taken 
at  random  should,  in  all  likelihood,  contain  a  population 
consisting  of  strains  with  different  degrees  of  resistance. 
If  a  high  but  not  the  maximal  concentration  of  an 
arsenic  compound  is  repeatedly  injected  into  the  in- 
fected mice  the  weaker  populations  of  trypanosomes 
are  killed  and  only  the  more  resistant  survive.  These 
of  course  continue  to  retain  their  resistance  if  trans- 
planted to  hosts  of  the  same  species.     According  to  this 


334  Adaptation  to  Environment 

interpretation  the  arsenic-fast  strain  may  possibly 
have  existed  before  the  experiments  were  made,  and 
Ehrlich's  treatment  consisted  only  in  eliminating  the 
less  resistant  strains. 

On  the  other  hand,  it  has  been  shown  that  if  an 
arsenic-fast  strain  of  trypanosomes  is  carried  through 
a  tetse  fly  it  loses  its  arsenic-fastness.  This  fact  may 
possibly  eliminate  the  applicability  of  the  pure  line 
theory  to  a  discussion  of  the  nature  of  the  arsenic- 
fastness,  but  it  seems  that  further  experiments  are 
desirable. 

5.  Dallinger  stated  that  he  succeeded  in  adapting 
certain  protozoans  to  a  temperature  of  70°  C.  by 
gradually  raising  their  temperature  during  several 
years.  It  is  desirable  that  this  statement  be  verified; 
until  this  is  done  doubts  are  justified.  Schottelius 
found  that  colonies  of  Micrococcus  prodigiosus  when 
transferred  from  a  temperature  of  22°  to  that  of  38° 
no  longer  formed  pigment  and  trimethylamine.  After 
the  cocci  had  been  cultivated  for  ten  or  fifteen  gen- 
erations at  38°  they  failed  to  form  pigment  even 
when  transferred  back  to  22°  C,  Dieudonne^  used 
Bacillus  Jluorescens  for  similar  purposes.  At  22°  it 
forms  a  fluorescing  pigment  and  trimethylamine,  but 
not  at  35°.  By  constantly  cultivating  this  bacillus 
at  35°  Dieudonne  found  that  after  the  fifteenth  genera- 
tion had  been  cultivated  at  35°  the  bacillus  produced 

*  Dieudonne,  A.,  Arh.  a.  d.  kais.  Gesndhtsmt.,  1894,  ix.,  492. 


Adaptation  to  Environment  335 

pigment  and  trimethylamine  at  35°.  Davenport  and 
Castle^  found  that  tadpoles  of  a  frog  kept  at  15°  went 
into  heat  rigour  at  40.3°  C,  while  those  kept  for  twenty- 
eight  days  at  25°  were  not  affected  by  this  temperature 
but  went  into  heat  rigour  at  43.5°.  When  the  latter 
tadpoles  were  put  back  for  seventeen  days  to  a  tem- 
perature of  15°  they  had  lost  their  resistance  to  high 
temperature  partially,  but  not  completely,  since  they 
went  into  heat  rigour  at  41.6°.  The  authors  suggest 
that  this  adaptation  to  a  higher  temperature  is  due  to 
a  loss  of  water  on  the  part  of  protoplasm,  whereby 
the  latter  becomes  more  resistant  to  an  increase  in 
temperature.  This  idea  was  put  to  a  test  by  Kryz% 
who  found  that  the  coagulation  temperature  of  their 
muscle  plasm  is  not  altered  by  keeping  cold-blooded 
animals  at  different  temperatures. 

Loeb  and  Wasteneys^  found  that  Fundulus  taken 
from  a  low  temperature  of  10°  C.  die  in  less  than  two 
hotus  when  suddenly  transferred  to  sea  water  of  29°  C. ; 
and  in  a  few  minutes  if  suddenly  transferred  to  a  tem- 
perature of  35°  C.  If,  however,  the  fish  were  trans- 
ferred to  a  temperature  of  27°  C.  for  forty  hours  they 
could  live  indefinitely  in  sea  water  of  35°.  By  exposing 
the  fish  each  day  two  hours  to  a  gradually  rising  tem- 


*  Davenport,  C.  B.,  and   Castle,   W.  E.,  Arch.  f.  Enlwcklngsmech., 
1896,  ii.,  227. 

*Kryz,  F.,  Arch.f.  Eniwcklngsmech.,  1907,  xxiii.,  560. 

3  Loeb,  J.,  and  Wasteneys,  H.,  Jour.  Exper.  ZooL,  1912,  xii.,  543. 


33^  Adaptation  to  Environment 

perature  they  could  render  them  resistant  to  a  tem- 
perature of  39°.  The  remarkable  fact  was  that  fish 
if  once  made  resistant  to  a  high  temperature  (35°)  did 
not  lose  this  resistance  when  kept  for  four  weeks  at 
from  10°  to  14°  C.  Control  fish  taken  from  the  same 
temperature  died  in  from  two  to  four  minutes;  im- 
munized fish  taken  from  10°  and  put  directly  to  35°  C. 
lived  for  many  hours  or  indefinitely.  They  will  even 
retain  this  immunity  when  kept  for  two  weeks  at  a 
temperature  of  0.4°  C. 

Why  is  it  that  an  animal  can  in  general  resist  a  high 
temperature  better  if  the  latter  is  raised  gradually 
than  when  it  is  raised  suddenly?  Physics  offers  us 
an  analogy  to  this  phenomenon  in  the  experience  that 
glass  vessels  which  burst  easily  when  their  temperature 
is  raised  suddenly,  remain  intact  when  the  temperature 
is  raised  gradually.  Glass  is  a  poor  conductor  of  heat 
and  when  the  temperature  is  raised  suddenly  inside  a 
glass  cylinder  the  inner  layer  of  the  cyhnder  expands 
while  the  outer  layer  on  account  of  the  slowness  of 
conduction  of  heat  does  not  expand  equally  and  the 
cyhnder  may  burst.  We  might  assume  that  the  sud- 
den increase  in  temperature  brings  about  certain  changes 
in  the  cells  {e.  g.,  an  increase  in  permeability  or  destruc- 
tion of  the  surface  layer?).  If  the  rise  of  temperature 
occurs  gradually  the  blood  or  lymph  or  the  cell  sap 
may  have  time  to  repair  the  damage,  and  this  repair 
seems  to  be  irreversible,  at  least  for  some  time,  as  the 


Adaptation  to  Environment  337 

experiments  on  Fundulus  seem  to  indicate.  If  the 
temperature  rises  too  rapidly  the  damage  cannot  be 
repaired  quickly  enough  by  the  cell  or  body  liquids. 

It  is  also  to  be  considered  that  substances  might 
be  formed  in  the  body  at  a  higher  temperature  which 
do  not  exist  at  a  lower  temperatiu-e,  and  vice  versa, 
and  this  might  explain  resiilts  Hke  those  of  Schottelius 
or  Dieudonne  and  many  others. 

6.  The  theory  of  an  adapting  effect  of  the  environ- 
ment has  often  been  linked  with  the  assumption  of  the 
inheritance  of  acquired  characters.  The  older  claims 
of  the  hereditary  transmission  of  acquired  characters, 
such  as  Brown-Sequard's  epilepsy  in  guinea  pigs  after 
the  cutting  of  the  sciatic  nerve,  have  been  shown  to  be 
imjustiiied  or  have  found  a  different  and  more  rational 
explanation.  Recently  P.  Kammerer  has  claimed  to 
have  proven  by  new  experiments  that  by  environmental 
changes,  hereditary  changes  can  be  produced. 

It  has  been  mentioned  already  that  the  mature  male 
frogs  and  toads  possess  during  the  breeding  season  lumps 
on  the  thumbs  or  arms  which  are  pigmented  and  which 
bear  numerous  minute  horny  black  spines ;  these  secon- 
dary sexual  characters  serve  the  male  frog  in  holding 
the  females  in  the  water  during  copulation.  There  is 
one  species  which  does  not  possess  this  sexual  character, 
namely  the  male  of  the  so-called  midwife  toad  (Alytes 
ohstetricans) .  In  this  species  the  animals  copulate  on 
land,  and  it  is  natural  to  connect  the  lack  of  this  secon- 


33^  Adaptation  to  Environment 

dary  sexual  character  in  the  male  with  its  different 
breeding  habit.  Kammerer  now  forced  such  toads  to 
copulate  in  water  instead  of  on  land  (by  keeping  the 
animals  in  a  terrarium  with  a  high  temperature).  He 
makes  the  statement  that  by  forcing  the  parents  to 
lay  their  eggs  during  successive  spawning  periods  in 
water  he  finally  obtained  offspring  which  under  normal 
temperature  conditions  lay  their  eggs  naturally  in 
water;  in  other  words,  they  have  changed  their  habits. 
We  will  not  discuss  this  part  of  his  statement  since 
the  breeding  habits  of  animals  in  captivity  are  Hable 
to  be  abnormal.  But  Kammerer  makes  the  further 
important  statement^  that  the  male  offspring  of  such 
couples  will  in  the  third  generation  produce  the  swell- 
ing on  the  thumb  and  the  usual  roughness,  and  in 
the  fourth  generation  black  pads  and  hypertrophy 
of  the  muscles  of  the  forearm  will  appear.  In  other 
words,  he  reports  having  succeeded  in  producing  an 
inheritance  of  an  acquired  morphological  character 
which  has  never  been  known  to  occur  in  this  species. 
Bateson,  on  account  of  the  importance  of  the  case, 
wished  to  examine  it  more  closely  and  I  will  quote  his 
report. 

The  systematists  who  have  made  a  special  study  of 
Batracliia  appear  to  be  agreed  that  Alytes  in  nature  does 
not  have  these  structures;  and  when  individuals  possessing 
them  can  be  produced  for  inspection  it  will,  I  think,  be  time 

'Kammerer,  P.,  Avh.J.  Entwcklngsmech.,  1909,  xxviii.,  448. 


Adaptation  to  Environment  339 

to  examine  the  evidence  for  the  inheritance  of  acquired 
characters  more  seriously.  I  wrote  to  Dr.  Kammerer  in 
July,  1 9 10,  asking  him  for  the  loan  of  such  a  specimen  and 
on  visiting  the  Biologische  Versuchsanstalt  in  September 
of  the  same  year  I  made  the  same  request,  but  hitherto 
none  has  been  produced.  In  matters  of  this  kind  much 
generally  depends  on  interpretations  made  at  the  time  of 
observation;  here,  however,  is  an  example  which  could 
readily  be  attested  by  preserved  material.^ 

More  recently  the  same  author  has  reported  another 
hereditary  morphological  change  brought  about  by 
outside  conditions.^  A  certain  salamander  {Salaman- 
dra  maculosa)  has  yellow  spots  on  a  generally  dark 
skin.  Kammerer  states  that  if  such  salamanders  are 
kept  on  a  yellow  ground  they  become  more  yellow, 
not  by  an  extension  of  the  chromatophores  (which  would 
not  be  surprising)  but  by  actual  multiplication  and 
growth  of  the  yellow  pigment  cells;  while  the  black 
skin  is  inhibited  in  its  growth.  The  reverse  is  true  if 
these  salamanders  are  kept  on  black  soil;  in  this  case 
according  to  Kammerer  the  growth  of  the  yellow  cells 
of  the  skin  is  inhibited  while  the  black  part  of  the  skin 
grows.  Curiously  enough,  according  to  him,  these  in- 
duced changes  are  hereditary.  Here  again  w^e  are  deal- 
ing with  the  inheritance  of  an  acquired  morphological 
character. 

'Bateson,  W.,  Problems  of  Genetics,  pp.  201-202.  Yale  University 
Press,  1913. 

'Kammerer,  P.,  Arch.  J.  Entwcklngsmech.,  1913,  xxxvi.,  4. 


340  Adaptation  to  Environment 

Megusar*  has  repeated  Kammerer's  experiments  on 
salamanders  but  contradicts  him  by  stating  that  the 
colour  of  the  soil  has  no  influence  on  the  colouration 
of  salamanders.  Of  course,  we  know  the  phenomenon 
of  colour  adaptation  in  which  the  animal  changes  its 
colour  pattern  according  to  the  environment.  This 
is  an  effect  of  the  retina  image  on  the  skin  and  has  been 
interpreted  by  the  writer  as  a  case  of  colour  tele- 
photography, for  which  no  physical  explanation  has 
yet  been  found.  ^  This  phenomenon,  however,  does  not 
lead  to  any  hereditary  change  of  colour. 

Kammerer  makes  many  statements  on  the  heredity 
of  acquired  modifications  of  instinct;  indeed  he  claims 
that  an  interest  in  music  on  the  part  of  parents  pro- 
duces offspring  with  musical  talent.  In  such  claims 
much  depends  upon  the  subjective  interpretation  of 
the  observer. 

The  writer  is  not  aware  that  there  Is  at  present  on 
record  a  single  adequate  proof  of  the  heredity  of  an 
acquired  character.  We  have  records  of  changes  in 
the  offspring  by  poisoning  the  germ  plasm  by  alcohol 
given  to  parents — as  in  Stockard's  well-known  experi- 
ments— or  by  exposing  butterflies  to  extreme  tempera- 
tures, but  in  these  cases  the  germ  cells  were  poisoned 
or  altered  by  the  alcohol  or  by  chemical  compounds 
produced  at  very  low  or  very  high  temperatures.     This 

'Werner,  F.,  Biol.  Centralbl.,  1915,  xxxv.,  176. 

'  Loeb,  J.,  The  Mechanistic  Conception  of  Life.     Chicago,  1912. 


Adaptation  to  Environment  341 

is  of  course  an  entirely  different  thing  from  stating 
that  by  inducing  the  midwife  toad  to  lay  its  eggs  in 
the  water  the  male  offspring  acquires  the  pads  and 
horns  of  other  species  of  frogs  on  its  thumb;  or  that 
by  keeping  black  salamanders  on  yellow  paper  the  off- 
spring is  more  yellow.  Yet  if  there  is  an  inheritance  of 
acquired  characters  which  can  in  any  way  throw  light 
on  the  so-called  phenomena  of  adaptation  it  must 
consist  in  results  such  as  Kammerer  claims  to  have 
obtained. 

While  the  writer  does  not  decline  to  accept  Ehrlich's 
interpretation  of  the  arsenic-fast  strains  of  trypano- 
somes  or  Kammerer's  statements  in  regard  to  the  inheri- 
tance of  acquired  character,  he  feels  that  more  work 
should  be  done  before  they  can  be  used  for  our  problem. 

7.  This  attitude  leaves  us  in  a  quandary.  The 
whole  animated  world  is  seemingly  a  symphony  of 
adaptation.  We  have  mentioned  already  the  eye 
with  its  refractive  media  so  well  curved  and  placed 
that  a  more  or  less  perfect  image  of  the  outside  objects 
is  focussed  exactly  on  the  retina;  and  this  in  spite  of 
the  fact  that  lens  and  retina  develop  independently; 
we  have  mentioned  and  discussed  the  cases  of  instincts 
or  automatic  arrangements  which  are  required  to  per- 
petuate life — the  attraction  of  the  two  sexes  and  the 
automatic  mechanisms  by  which  sperm  and  egg  are 
brought  together;  the  maternal  instincts  by  which  the 
young  are  taken  care  of;  and  all  those  adaptations  by 


342.         Adaptation  to  Environment 

which  animals  get  their  food  and  the  suitable  conditions 
of  preservation.  Can  we  understand  all  these  adapta- 
tions without  a  belief  In  the  heredity  of  acquired  char- 
acters? As  a  matter  of  fact  the  tenacity  with  which 
some  authors  cling  to  such  a  belief  Is  dictated  by  the 
idea  that  this  is  the  only  alternative  to  the  supra- 
naturalistic  or  vitalistic  Ideas.  The  writer  is  of  the 
opinion  that  we  do  not  need  to  depend  upon  the  as- 
sumption of  the  heredity  of  acquired  characters,  but  that 
physiological  chemistry  Is  adequate  for  this  purpose. 

The  earlier  writers  explained  the  growth  of  the  legs 
in  the  tadpole  of  the  frog  or  toad  as  a  case  of  an  adapta- 
tion to  life  on  land.  We  know  through  Gudernatsch 
that  the  growth  of  the  legs  can  be  produced  at  any 
time  even  In  the  youngest  tadpole,  which  is  unable  to 
live  on  the  land,  by  feeding  the  animal  with  the  thyroid 
gland.  As  we  have  stated  In  Chapter  VII,  it  Is  quite 
possible  that  In  nature  the  legs  of  the  tadpole  begin  to 
grow  when  enough  of  the  thyroid  or  a  similar  compound 
has  been  formed  or  is  circulating  In  the  animal. 

It  might  justly  be  claimed  as  a  case  of  adaptation 
that  the  egg  attaches  itself  to  the  wall  of  the  uterus 
and  calls  forth  the  formation  of  the  decidua.  We 
have  mentioned  the  observation  of  Leo  Loeb  that  the 
corpus  luteum  of  the  ovary  gives  off  a  substance  to  the 
blood  which  alters  the  tissues  in  the  uterus  In  such  a 
way  that  contact  with  any  foreign  body  {e.  g.,  the  egg) 
induces  this  decidua  formation.     Again  what  appeared 


Adaptation  to  Environment  343 

as  adaptation  when  unknown  turns  out  to  be  a  result 
of  the  action  of  a  definite  chemical  substance  circulating 
in  the  body. 

It  appears  as  a  case  of  adaptation  that  the  eggs  of 
the  majority  of  animals  cannot  develop  without  a 
spermatozoon,  and  yet  we  can  imitate  the  activating 
effect  of  a  spermatozoon  on  the  egg  by  definite  chemical 
compounds,  which  leads  to  the  suggestion  that  the 
activating  effect  of  the  spermatozoon  on  the  egg  might 
be  due  to  the  fact  that  it  carries  such  a  compound. 

The  wonderful  adaptations  exhibited  in  the  mating 
instincts  seem  to  be  due  to  definite  substances  secreted 
by  the  sex  glands,  as  was  shown  by  Steinach  (Chapter 
VII) .  Here,  again,  the  process  as  popularly  conceived, 
is  the  reverse  of  the  truth;  those  survive  that  have  the 
equipment, — they  did  not  acquire  the  equipment  under 
the  influence  of  environment. 

It  is  absolutely  imperative  for  green  plants  that  their 
stems  and  leaves  be  exposed  to  the  light  since  only  in 
this  way  are  they  able  to  form  carbohydrates;  and  it  is 
equally  essential  that  the  roots  should  grow  into  the  soil 
so  that  the  plant  may  get  the  nitrates  and  phosphates 
required  to  build  up  its  proteins  and  nucleins.  This 
result  is,  in  the  language  of  adaptationists,  brought 
about  by  an  adaptive  response  of  the  plant  to  the  light. 
In  reality  this  adaptive  response  is  due  (Chapter  X) 
to  the  presence  of  a  photosensitive  substance  present 
in  almost  all  green  plants. 


344  Adaptation  to  Environment 

Lewis  has  shown  that  if  the  optic  cup  is  transplanted 
under  the  skin  of  a  young  larva  into  any  part  of  the 
body  the  skin  in  contact  with  the  optic  cup  will  form 
a  lens;  it  looks  as  if  a  chemical  substance  from  the 
optic  cup  were  responsible  for  the  formation  of  the  lens. 

These  examples  might  be  multiplied  indefinitely. 
They  all  indicate  that  apparent  morphological  and 
instinctive  adaptations  are  merely  caused  by  chemical 
substances  formed  in  the  organism  and  that  there  is 
no  reason  for  postulating  the  inheritance  of  acquired 
characters.  We  must  not  forget  that  there  are  just 
as  many  cases  where  chemical  substances  circulating 
in  the  body  lead  to  indifferent  or  harmful  results.  As 
an  example  of  the  first  type,  we  may  mention  the  exist- 
ence of  heliotropism  in  animals  living  in  the  dark,  of 
the  latter  type,  the  inheritance  of  deficiencies  like 
colour-blindness  or  glaucoma. 

While  it  is  possible  for  forms  with  moderate  dis- 
harmonies to  survive,  those  with  gross  disharmonies 
cannot  exist  and  we  are  not  reminded  of  their  possible 
existence.  As  a  consequence  the  cases  of  apparent 
adaptation  prevail  in  nature. 

The  following  observation  may  serve  to  give  an  idea 
how  small  is  the  number  of  existing  or  durable  forms 
compared  with  the  number  of  forms  incapable  of  exist- 
ence. We  have  mentioned  the  fact  observed  by  Moenk- 
house,  the  writer,  and  Newman,  that  it  is  possible  to 
fertilize  the  eggs  of  each  marine  bony  fish  with  the 


Adaptation  to  Environment  345 

sperm  of  practically  every  other  marine  bony  fish. 
The  number  of  teleosts  at  present  in  existence  is  about 
ten  thousand.  If  we  accomplish  all  possible  hybridiza- 
tions, one  hundred  million  different  crosses  will  result. 
Of  these  only  a  small  fraction  of  one  per  cent,  can  live 
(see  Chapter  I),  and  it  is  generally  the  lack  of  a 
proper  circulation  which  inhibits  them  from  reaching 
maturity.  It  is,  therefore,  no  exaggeration  to  state 
that  the  nimiber  of  species  existing  today  is  only  an 
extremely  small  fraction  of  those  which  can  and  pos- 
sibly do  originate,  but  which  escape  our  notice  and 
disappear  because  they  cannot  Hve  or  reproduce.  If 
we  consider  these  facts  we  realize  that  the  mere  laws 
of  chance  are  adequate  to  account  for  the  fact  of  the 
apparently  purposeful  adaptations;  as  they  are  ade- 
quate to  account  for  the  Mendelian  numbers. 


CHAPTER  XIII 

EVOLUTION 

Darwin's  work  has  been  compared  to  that  of  Coper- 
nicus and  Galileo  inasmuch  as  all  these  men  freed  the 
mind  from  the  incubus  of  Aristotelian  philosophy  which, 
with  the  efficient  co-operation  of  the  church  and  the 
predatory  system  of  economics,  caused  the  stag- 
nation, squalor,  immorality,  and  misery  of  the 
Middle  Ages.  Copernicus  and  Galileo  were  the 
first  to  deliver  the  intellect  from  the  idea  of  a  uni- 
verse created  for  the  purpose  of  man;  and  Darwin 
rendered  a  similar  service  by  his  insistence  that 
accidental  and  not  purposeful  variations  gave  rise 
to  the  variety  of  organisms.  In  this  struggle  for 
intellectual  freedom  the  names  of  Huxley  and  Haeckel 
must  be  gratefully  remembered,  since  without  them 
Darwin's  idea  would  not  have  conquered  hu- 
manity. 

Darwin  assumed  that  the  small  fluctuating  variations 

could  accumulate  to  larger  variations  and  thus  cause 

new  forms  to  originate. 

346 


Evolution  347 

It  was  the  merit  of  de  Vries^  to  have  pointed  out  that 
fluctuating  variations  are  not  hereditary  and  hence 
could  not  have  played  the  r61e  assigned  to  them  by 
Darwin,  while  discontinuous  variations  as  they  appear 
in  the  so-called  "sports"  or  mutations  are  inherited. 
This  was  an  important  step  in  the  history  of  the  theory 
of  evolution.  It  did  not  touch  the  foundation  of  Darwin's 
work,  namely  the  substitution  of  the  idea  of  an  acci- 
dental evolution  for  that  of  a  purposeful  creation;  it 
only  modified  the  conception  of  the  possible  mechanism 
of  evolution.  According  to  de  Vries,  there  are  special 
species  or  groups  of  species  which  are  in  a  state  of  muta- 
tion. He  considers  the  evening  primrose  on  which  he 
made  his  observations  as  one  of  these  forms.  Morgan 
and  his  pupils  have  observed  over  130  mutations  in  a 
fly  Drosophila.  From  our  present  limited  knowledge  we 
must  admit  the  possibility  that  the  tendency  toward  the 
production  of  mutants  is  not  equally  strong  in  different 
forms.  Whether  this  part  of  de  Vries's  idea  is  or  is  not 
correct  there  can  be  no  doubt  that  variations  occur  which 
consist  in  the  loss  and  apparently,  though  in  rarer  cases, 
in  the  gain  or  a  modification  of  a  Mendelian  factor.  If  we 
wish  to  visualize  the  basis  of  such  a  change  we  may  do  so 
by  imagining  well-defined  chemical  constituents  in  one  or 
more  of  the  chromomeres  undergoing  a  chemical  change. 

'  de  Vries,  H.,  The  Mutation  Theory,  translated  by  Farmer,  J.  B., 
and  Darbishire,  A.  D.,  Chicago,  1909.  Species  and  Varieties.  Chicago, 
1906.     Gruppenweise  Artbildung.     Berlin,  1913. 


34^  Evolution 

This  way  of  looking  at  the  origin  of  variation  has 
had  the  effect  of  putting  an  end  to  the  vague  specula- 
tions concerning  the  evolution  of  one  form  from  another. 
We  demand  today  the  experimental  test  when  such  a 
statement  is  made  and  as  a  consequence  the  amount 
of  mere  speculation  in  this  field  has  diminished 
considerably. 

It  is  possible  that  any  further  progress  concerning 
evolution  must  come  by  experimental  attempts  to 
bring  about  at  will  definite  mutations.  Such  attempts 
have  been  reported  but  they  are  not  all  beyond  the 
possibility  of  error.  ^  The  most  remarkable  among 
them  are  those  by  Tower  who  by  a  very  complicated 
combination  of  effects  of  temperature  and  moisture 
claims  to  have  produced  definite  mutations  in  the 
potato  beetle.  The  conditions  for  these  experiments 
are  so  expensive  and  complicated  that  a  repetition  by 
other  investigators  has  not  yet  been  possible. 

It  is,  however,  still  uncertain  whether  the  mere  addi- 
tion or  loss  of  IMendelian  characters  can  lead  to  the 
origin  of  new  species.  Species  specificity  Is  determined 
by  specific  proteins  (Chapter  III.),  while  some  Mende- 
lian  characters  at  least  seem  to  be  determined  by  hor- 
mones or  substances  which  need  neither  be  proteins  nor 
specific  for  the  species. 

'  For  a  critical  discussion  of  the  details,  see  Bateson,  W.,  Problems 
of  Genetics,  New  Haven,  1913,  Chapter  X. 


CHAPTER  XIV 

DEATH  AND  DISSOLUTION  OF  THE  ORGANISM 

I.  It  is  an  old  saying  that  we  cannot  understand 
life  unless  we  understand  death.  The  dead  body,  if 
its  temperature  is  not  too  low  and  if  it  contains  enough 
water,  undergoes  rapid  disintegration.  It  was  natural 
to  argue  that  life  is  that  which  resists  this  tendency  to 
disintegration.  The  older  observers  thought  that  the 
forces  of  nature  determined  the  decay,  while  the  vital 
force  resisted  it.  This  idea  found  its  tersest  expres- 
sion in  the  definition  of  Bichat,  that  "Hfe  is  the  sum 
total  of  the  forces  which  resist  death."  Science  is  not 
the  field  of  definitions,  but  of  prediction  and  control. 
The  problem  is:  first,  how  does  it  happen  that  as  soon 
as  respiration  has  ceased  only  for  a  few  minutes  the 
human  body  is  dead,  that  is  to  say,  will  commence  to 
undergo  disintegration,  and  second,  what  protects  the 
body  against  this  decay  while  the  respiration  goes  on, 
although  temperature  and  moisture  are  such  as  to 
favour  decay? 

The  earlier  biologists  had  already  raised  the  question 

349 


350  Death  and  Dissolution  of  the  Organism 

why  it  was  that  the  stomach  and  intestine  did  not 
digest  themselves.  The  hydrochloric  acid  and  the 
pepsin  in  the  stomach  and  the  trypsin  in  the  intestine 
digest  proteins  taken  in  in  the  form  of  food;  why  do 
they  not  digest  the  proteins  of  the  cells  of  the  stomach 
and  the  intestine?  They  will  promptly  digest  the 
stomach  as  soon  as  the  individual  is  dead,  but  not  during 
life.  A  self-digestion  may  also  be  caused  if  the  arteries 
of  the  stomach  are  ligatured.  Claude  Bernard  and 
others  suggested  that  the  layer  of  mucus  protected 
the  cells  of  the  stomach  and  of  the  intestme  from  the 
digestive  enzymes;  or  that  the  epithelial  layer  had  a 
protective  effect.  Pavy  suggested  that  the  alkali  of 
the  blood  had  a  protective  action.  All  these  theories 
became  untenable  when  Fermi  showed  that  all  kinds 
of  living  organisms,  protozoans,  worms,  arthropods, 
are  not  digested  in  solutions  of  trypsin  as  long  as  they 
are  alive,  while  they  are  promptly  digested  in  the  same 
solution  when  dead.^  This  is  in  harmony  with  the 
fact  that  many  parasites  live  in  the  intestine  without 
being  digested  as  long  as  they  are  alive.  Fermi  con- 
cluded that  the  living  cell  cannot  be  attacked  by  the 
digestive  ferments,  while  with  death  a  change  occurs 
by  which  they  can  be  attacked.  But  what  is  this 
change?  Fermi  seems  to  be  inclined  to  think  that  the 
"living  molecule"  of  protein  is  not  hydrolysable  (per- 
haps because  the  enzyme   cannot  attach  itself  to  it?), 

'Fermi,  C,  Centralbl.  f.  Bacteriologie,  Abt.  i,  1910,  Ivi.,  55. 


Death  and  Dissolution  of  the  Organism  351 

while  a  change  in  the  constitution  or  configuration  of 
the  proteins  takes  place  after  respiration  has  ceased. 
The  fact  that  the  living  cell  resists  the  digestive  action 
of  trypsin  and  pepsin  has  found  two  other  modes  of 
explanation,  first,  that  the  cells  are  surrounded  by  a 
membrane  or  envelope  through  which  the  enzyme  can- 
not diffuse,  and  second,  that  the  living  cells  possess 
antiferments.  But  the  so-called  antiferments  are 
also  said  to  exist  after  the  death  of  the  cell,  whereas 
after  death  the  cell  is  promptly  digested.  Fredericq, 
as  well  as  Klug,  has  shown  that  worms  which  are  not 
attacked  by  trypsin  are  digested  by  this  enzyme  when 
they  are  cut  into  small  pieces;  although  the  pieces 
of  course  contain  the  antienzyme.  The  other  sugges- 
tion that  a  membrane  impermeable  for  trypsin  protects 
the  cells  would  explain  why  livmg  protozoa  are  not 
digested  by  trypsin,  but  it  leaves  another  fact  unex- 
plained, namely,  the  autodigestion  of  all  the  cells  after 
death  by  enzymes  contained  in  the  cells  themselves. 

2.  The  disintegration  of  the  body  after  death  is  not 
caused  exclusively  or  even  chiefly  by  the  digestive  en- 
zymes of  the  intestinal  tract  or  the  micro-organisms  enter- 
ing the  dead  body  from  the  outside,  but  by  the  enzymes 
contained  in  the  cells  themselves.  This  phenomenon  of 
autolysis^  was  first  characterized  by  Hoppe-Seyler. ^ 

^  Levene,  P.  A.,  Autolysis.  The  Harvey  Lectures,  1905-1906,  p.  73, 
gives  a  full  account  of  the  work  on  this  subject  up  to  1905. 

^  Hoppe-Seyler,  F.,  Tiihinger  med.-chem.  Untersuchungen,  1871,  p.  499. 


352  Death  and  Dissolution  of  the  Organism 

All  organs  suffering  death  within  the  organism,  in  the 
absence  of  oxygen,  undergo  softening  and  dissolution  in  a 
manner  resembling  that  of  putrefaction.  In  the  course  of 
that  process,  albuminous  matter  gives  rise  to  leucin  and 
tyrosin,  fat  to  free  acids  and  soaps.  This  maceration,  iden- 
tical with  the  pathological  conception  of  softening,  is  ac- 
complished without  giving  rise  to  ill  odour  and  is  a  process 
similar  to  the  one  resulting  from  the  action  of  water,  acids, 
and  digestive  enzymes. 

In  work  of  this  kind,  rigid  asepsis  is  required  to 
exclude  the  possibility  of  bacterial  infection  and  this 
was  first  done  by  Salkowski,  who  showed  that  in 
aseptically  kept  tissues  hke  liver  and  muscle  the  amount 
of  substances  that  can  be  extracted  with  hot  water 
increases  considerably.  By  the  work  of  others,  especi- 
ally Ivlartin  Jacoby  and  Levene,  it  was  established  that 
the  power  of  self-digestion  is  shared  by  all  organs. 
Analysis  of  the  products  of  the  autodigestion  of  tissues 
shows  that,  e.  g.,  the  amino  acids,  which  constitute  the 
proteins,  are  produced.  Dakin,  Jones,  and  Levene 
demonstrated  the  hydrolytic  products  of  the  nucleins, 
in  the  case  of  the  self-digestion  of  tissues.  ^ 

Again  the  question  arises:  Why  do  the  tissues  not 
undergo  autolysis  during  hfetime  and  what  protects 
them,  and  the  answer  is  that  self-digestion  is  a  conse- 
quence of  the  lack  of  oxidations.  The  presence  of 
antiferments  must  continue  after  death  and  cannot 
be  the  cause  which  prevents  the  self-digestion  during 

*  Levene,  P.  A.,  Am.  Jour.  Physiol.,  1904,  xii.,  276. 


Death  and  Dissolution  of  the  Organism  353 

life,  since  nothing  indicates  the  destruction  of  the 
hypothetical  antidigestive  enzymes  through  lack  of 
oxygen.  The  recent  work  of  Bradley  and  Morse  ^ 
and  of  Bradley^  has  thrown  some  light  on  the  problem. 
These  authors  found  that  proteins  of  the  liver  which 
are  indigestible  can  be  made  digestible  by  the  liver 
enzymes  if  an  acid  salt  or  a  trace  of  acid  is  added  to 
the  mixture.  A  m/200  HCl  solution  gives  marked 
acceleration  of  the  autodigestion  of  the  liver.  This 
would  explain  why  autodigestion  takes  place  after 
oxidations  cease.  In  many  if  not  all  the  cells,  acids 
are  constantly  formed  during  lifetime,  e.  g.,  lactic  acid, 
which  through  oxidation  are  turned  to  CO  2,  and  this 
diffuses  into  the  blood  so  that  the  H  ion  concentration 
in  the  cells  does  not  rise  materially.  If,  however,  the 
oxidations  cease,  as  is  the  case  after  death,  the  forma- 
tion of  lactic  acid  continues,  but  the  acid  is  not  oxidized 
to  CO  2  and  thus  removed,  and  as  a  consequence  the 
H  ion  concentration  increases  in  the  cells  and  the  self- 
digestion  of  proteins,  which  the  digestive  enzymes  con- 
tained in  the  cells  themselves  could  not  attack  formerly, 
becomes  possible.  Acid  increases  the  digestibility 
of  a  protein,  probably  by  salt  formation.  Theoreti- 
cally we  should  not  be  surprised  that  while  in  the  liver 
an  increase  in  the  Ch  favours  autolysis  in  other  tissues 
the  same  result  is  produced  by  the  reverse  effect.     We 

'  Bradley  H.  C,  and  Morse,  M.,  Jour.  Biol.  Chem.,  1915,  xxi.,  209. 
*  Bradley,  H.  C,  ibid.,  1915,  xxii.,  113. 
23 


354  Death  and  Dissolution  of  the  Organism 

might  say  that  the  preservation  of  a  certain  Ch  prob- 
ably at  or  near  the  point  of  neutrality  during  life  pre- 
vents self-digestion,  while  the  gross  alteration  of  the 
Ch  in  either  direction  after  death  (or  after  the  cessa- 
tion of  oxidations  in  the  tissues)  induces  autolysis. 
Bradley  indeed  suggests  that  many  of  the  phenomena 
of  autolysis  during  lifetime,  such  as  atrophy,  necrosis, 
involution,  might  be  due  to  an  increase  in  the  Ch  in 
the  tissues. 

These  facts  agree  with  the  suggestion  of  Fermi  that 
in  the  living  cell  the  proteins  cannot  be  attacked  by 
the  digestive  enzymes  but  relieves  us  of  the  necessity 
of  making  the  monstrous  assumption  of  a  "living 
molecule"  of  proteins  as  distinct  from  a  "dead"  mole- 
cule. The  difference  between  life  and  death  is  not  one 
between  living  and  dead  molecules,  but  more  likely 
between  the  excess  of  synthetic  over  hydrolytic 
processes. 

In  the  second  chapter  we  mentioned  the  interesting 
idea  of  Armstrong  that  when  a  synthesis  is  brought 
about  by  a  digestive  enzyme  {e.  g.,  maltase)  not  the 
original  substrate  is  formed  {e.  g.,  maltose)  but  an 
isomer,  in  this  case  isomaltose;  and  this  isomer  is  not 
attacked  by  the  enzyme  maltase.  We  thus  get  a 
rational  understanding  of  the  statement  which  Claude 
Bernard  used  to  make  but  which  remained  at  his  time 
mysterious:  la  vie,  c'est  la  creation.  During  life, 
when    nutritive   material    is   abundant,    through   the 


Death  and  Dissolution  of  the  Organism  355 

reversible  action  of  certain  enzymes,  synthetic  com- 
pounds are  formed  from  the  building  stones  furnished 
by  the  blood.  These  synthetic  isomers  cannot  be 
hydrolyzed  by  the  enzymes  by  which  they  are  formed 
and  hence  on  account  of  the  isomeric  structure  are 
immune  against  destruction.  It  is  not  impossible  that 
the  increase  of  the  concentration  of  acid  in  the  cells 
after  death  transforms  the  isomers  into  that  form  in 
which  they  can  be  digested  by  the  enzymes  contained 
in  the  cell.  Another  possibility  is  that  the  increase  in 
digestibility  brought  about  by  an  increase  in  Ch  in 
the  cell  is  due  to  the  hydrating  effect  of  acids  on  proteins 
with  a  subsequent  increase  in  digestibility.  Whatever 
the  answer  may  be,  the  work  done  since  Claude  Bernard 
has  removed  that  cloud  of  obscurity  which  in  his  days 
surrounded  the  prevalence  of  synthetic  action  in  the 
living  and  of  disintegration  in  the  dead  tissues. 

3.  We  have  already  referred  to  the  connection 
between  the  lack  of  oxygen  and  the  onset  of  autolysis 
and  disintegration  of  tissues  in  the  body.  It  is  of 
interest  that  there  are  cells  in  which  the  disintegration 
under  the  influence  of  lack  of  oxygen  is  so  rapid  that 
it  can  be  followed  under  the  microscope.  The  writer 
has  observed  that  certain  cells  undergo  complete  irre- 
versible dissolution  in  a  very  short  time  under  the 
influence  of  lack  of  oxygen,  e.  g.,  the  first  segmentation 
cells  of  the  egg  of  a  teleost  fish  Ctenolahrus .  ^ 

^  Loeb,  J.,  Arch.f.  d.  ges.  Physiol.,  1895,  Ixii.,  249. 


35^  Death  and  Dissolution  of  the  Organism 

When  these  eggs  are  deprived  of  oxygen  at  the  time  they 
reach  the  eight-  or  sixteen-cell  stage,  it  can  be  noticed  that 
the  membranes  of  the  blastomeres  are  transformed  into 
small  droplets  within  half  an  hour  or  more,  according  to 
the  temperature.  These  droplets  begin  to  flow  together, 
forming  larger  drops.     [Figures  48  to  51  show  the  successive 


Fig.  48 


Fig.  49 


•*. . 


..^fe 


FIG.  50 


Fig.  51 


Stages  of  this  process.]    When  the  eggs  are  exposed  to  the 

air  in  time,  segmentation  can  begin  again;  but  if  a  slightly 
longer  time  is  allowed  to  elapse,  the  process  becomes  irre- 
versible and  life  becomes  extinct.  Such  clear  structural 
changes  cannot  often  be  observed  in  the  eggs  of  other 
animals  under  the  same  conditions.  Are  these  changes  of 
Structure  (apparently  liquefaction  of  solid  elements)  respon- 
sible for  death  under  such  conditions?  In  order  to  obtain 
an  answer  to  this  question,  the  writer  investigated  the 


Death  and  Dissolution  of  the  Organism  357 

effect  of  the  lack  of  oxygen  upon  the  heart-beat  of  the  em- 
bryo of  the  same  fish  Ctenolabrus.  This  egg  is  perfectly 
transparent  and  the  heart-beat  can  easily  be  watched. 
When  these  eggs  are  put  into  an  Engelmann  gas  chamber 
and  a  current  of  pure  hydrogen  is  sent  through,  the  heart 
may  cease  to  beat  in  fifteen  or  twenty  minutes;  it  stops 
beating  suddenly,  before  the  number  of  heart-beats  has 
diminished  noticeably,  and  ceases  beating  before  all  the 
free  oxygen  can  have  had  time  to  diffuse  from  the  egg. 
In  one  case  the  heart  beat  ninety  times  per  minute  before 
the  hydrogen  was  sent  through;  four  minutes  after  the 
current  of  hydrogen  had  passed  through  the  gas  chamber, 
the  rate  of  the  heart-beat  was  eighty-seven  per  minute, 
three  minutes  later  it  was  seventy-seven,  and  then  the 
beats  stopped  suddenly.  It  is  hard  to  believe  that  this 
cessation  could  have  been  caused  by  lack  of  energy. 
Hydrolytic  processes  alone  could  furnish  sufficient  energy  to 
maintain  the  heart-beat  for  some  time,  even  if  all  the  oxygen 
had  been  used  up.  The  suddenness  of  the  standstill  at  a 
time  when  the  rate  had  hardly  diminished  seems  to  be 
more  easily  explained  by  a  sudden  collapse  of  the  machine; 
it  might  be  that  liquefaction  or  some  other  change  of 
structure  occiirs  in  the  heart  or  its  ganglion  cells,  compar- 
able to  that  which  we  mentioned  before.  In  another  fish 
Fundulus,  where  the  cleavage  cells  undergo  no  visible 
changes  in  the  case  of  lack  of  oxygen,  the  heart  of  the  em- 
bryo can  continue  to  beat  for  about  twelve  hours  in  a  cur- 
rent of  hydrogen.  In  this  case  the  rate  of  the  heart-beat 
sinks  during  the  first  hour  in  the  hydrogen  current  from 
about  one  hundred  to  twenty  or  ten  per  minute;  then  it 
continues  to  beat  at  this  rate  for  ten  hours  or  more.  In 
this  case  one  might  believe  that  during  the  period  of  steady 
diminution  of  the  tension  of  oxygen  in  the  heart  (during 
the  first  hour),  the  heart-beat  sinks  steadily  while  it  keeps 
up  at  a  low  but  steady  rate  as  long  as  the  energy  for  the 


35^^  Death  and  Dissolution  of  the  Organism 

beat  is  supplied  solely  by  hydrolytic  processes;  but  there 
is  certainly  no  change  in  the  physical  structure  of  the  cells 
noticeable  in  Fimdulus,  and  consequently  there  is  no  sudden 
standstill  of  the  heart. 

Budgett  has  observed  that  in  many  infusorians  visible 
changes  of  structure  occur  in  the  case  of  lack  of  oxygen^; 
as  a  rule  the  membrane  of  the  infusorian  bursts  or  breaks 
at  one  point,  whereby  the  liquid  contents  flow  out.  Har- 
desty  and  the  writer  found  that  Paramoecium  becomes  more 
strongly  vacuolized  when  deprived  of  oxygen,  and  at  last 
bursts.  Amcebas  likewise  become  vacuolized  and  burst 
under  these  conditions.  Budgett  found  that  a  number  of 
poisons,  such  as  potassium  cyanide,  morphine,  quinine, 
antipyrine,  nicotine,  and  atropine,  produce  structural 
changes  of  the  same  character  as  those  described  for  lack 
of  oxygen.  As  far  as  KCN  is  concerned,  Schoenbein  had 
already  observed  that  it  retards  the  oxidation  in  the  tissues, 
and  Claude  Bernard  and  Geppert  confirmed  this  observa- 
tion. For  the  alkaloids,  W.  S.  Young  has  shown  that  they 
are  capable  of  retarding  certain  processes  of  autoxidation. 
This  accounts  for  the  fact  that  the  above-mentioned  poisons 
produce  changes  similar  to  those  observed  in  the  case  of  lack 
of  oxygen.^ 

The  phenomenon  of  rapid  disintegration  when  de- 
prived of  oxygen  (or  in  the  presence  of  KCN)  seems  to 
be  general  as  Child  ^  has  shown  in  extensive  experiments. 
Child  has  used  it  to  show  that  younger  animals  disin- 
tegrate more  rapidly  than  older  or  larger  ones,  and  he 
uses  this  fact  for  a  theory  of  senescence.     He  connects 

'  Budgett,  S.  P.,  Am.  Jour.  Physiol.,  1898,  i.,  210." 
'  Loeb,  J.,  The   Dynamics  of  Living   Matter,  New  York,  1906,  pp. 
19-21, 

3  Child,  CM.,  Senescence  and  Rejuvenescence.     Chicago,  1915. 


Death  and  Dissolution  of  the  Organism  359 

the  more  rapid  disintegration  of  the  young  animal  with 
a  greater  metaboHsm.^  Without  wishing  to  doubt 
Child's  interesting  observations  the  writer  is  not 
quite  certain  whether  the  more  rapid  disintegration 
of  the  younger  forms  is  not  a  result  of  the  fact  that  the 
walls  of  membranes  in  the  young  are  softer  than  those 
of  the  older  animals,  and  hence  are  more  readily  lique- 
fied. Such  a  difference  could  be  due  to  mere  chemical 
constitution,  e.  g.,  the  increase  in  Ca  in  the  membrane 
with  the  increase  in  age.  In  old  age  in  man  the  deposit 
of  Ca  in  the  blood-vessels  is  a  frequent  occurrence. 

These  facts  may  help  us  to  understand  the  nature  of 
death  and  dissolution  of  the  body  in  higher  animals. 
Death  in  these  animals  is  due  to  cessation  of  oxidations, 
but  the  surprising  fact  is  that  if  the  oxidations  have 
been  interrupted  but  a  few  minutes  life  cannot  be 
restored  even  by  artificial  respiration.  This  suggests 
that  the  respiratory  ganglia  in  the  medulla  oblongata 
suffer  an  irreparable  injury  or  an  irreversible  change 
(comparable  to  that  just  described  in  the  cells  of  Cteno- 
labrus)  even  when  deprived  of  oxygen  for  only  a  short 
time.  As  a  consequence  of  the  irreversible  injury  to 
the  medulla  the  respirations  cease  permanently,  the 

*  It  is  a  fact  that  in  the  early  cells  of  Ctenolabrus  the  dissolution  of 
the  cell  walls  through  lack  of  O  precedes  death,  since  when  oxygen  is 
admitted  early  enough  the  cells  recover  again.  In  infusorians  the 
bursting  of  the  animal  due  to  lack  of  O  occurs  suddenly,  while  the  animal 
is  still  moving,  and  this  bursting  is  the  cause  of  death,  and  not  the 
reverse. 


360  Death  and  Dissolution  of  the  Organism 

heart-beat  must  also  cease,  and  gradually  the  different 
tissues  must  undergo  the  dissolution  characteristic 
of  death.  While  all  the  cells  may  be  immortal  they 
are  only  so  in  the  presence  of  oxygen  and  the  nutritive 
solution  which  the  circulating  blood  furnishes.  With 
the  proper  supply  of  oxygen  cut  off  they  can  no  longer 
live. 

4.  It  IS  an  unquestionable  fact  that  each  form  has 
a  quite  definite  duration  of  life.  Unicellular  organisms 
are  immortal ;  but  for  the  higher  organisms  with  sexual 
reproduction  the  duration  of  life  is  almost  as  character- 
istic as  any  morphological  peculiarity  of  a  species. 
No  species  can  exist  unless  the  natural  life  of  its  in- 
dividuals outlasts  the  period  of  sexual  maturity;  and 
unless  the  average  duration  of  life  is  long  enough  to 
allow  as  many  offspring  to  be  brought  into  the  world 
as  will  compensate  for  loss  by  death.  The  male  bee 
dies  before  it  is  a  year  old,  while  the  queen  may  live 
several  years.  In  a  certain  species  of  butterflies,  the 
PsychidcC,  the  parthenogenetic  female  lays  its  eggs 
while  still  in  the  cocoon  and  then  dies  without  ever 
leaving  the  cocoon.  The  imago  of  the  ephemera 
leaves  the  water  in  the  evening,  copulates,  lets  its  eggs 
fall  into  the  water,  and  is  dead  the  next  morning.  The 
imperfect  condition  of  their  mandibles  and  alimentary 
canal  makes  them  unfit  for  a  long  duration  of  life.  The 
males  of  the  rotifers  which  are  devoid  of  organs  of 
digestion  live  but  a  few  days. 


Death  and  Dissolution  of  the  Organism  361 

In  the  Zoological  Station  at  Naples  in  1906,  an 
actinian,  Actinia  equina,  was  alive  after  having  been 
in  captivity  fifteen  years,  and  another  one,  Cerianthus, 
had  been  observed  for  twenty-four  years.  Korschelt 
kept  earthworms  for  as  long  as  ten  years.  The  fresh- 
water mussel  may  reach  the  age  of  sixty  years  or  more 
and  crayfish  may  live  for  over  twenty  years.  The 
differences  in  the  duration  of  life  of  mammals  are  too 
well  known  to  need  discussion.  If  the  cells  and  tissues 
are  immortal,  how  does  it  happen  that  the  duration 
of  life  is  so  characteristic  for  each  species? 

Metchnikoff  ^  has  recently  investigated  the  cause  of 
** natural"  death  in  the  butterfly  of  the  silkworm.  The 
butterfly  in  this  species  lacks  the  organs  necessary  for 
taking  up  food,  like  the  male  rotifer  or  the  ephemeridse 
and  hence  is  already,  by  this  fact,  condemned  to  a 
short  life.  Metchnikoff  observed  that  these  butterflies 
could  live  twenty- three  days,  but  the  average  duration 
of  life  was  15.6  for  the  males  and  16.6  days  for  the 
females;  and  that  seventy-five  per  cent,  of  them  con- 
tained no  parasitic  fauna  or  flora  in  their  intestine. 
They  lose  considerably  in  weight  during  their  lives, 
but  the  males  still  contain  the  fat  body  at  the  time  of 
death.  None  of  the  changes  accompanying  "old  age" 
in  man  are  found  in  the  tissues  of  these  butterflies 
before  death.  Metchnikoff  is  inclined  to  believe  that 
the  animal  is  poisoned  by  some  excretion  retained  in 
^  Metchnikoff,  E.,  Ann.  d.  VInst.  Pasteur,  1915,  xxix.,  477. 


362  Death  and  Dissolution  of  the  Organism 

the  body;  namely,  the  urine,  and  that  this  poison  also 
causes  the  symptoms  of  weakness  which  characterize 
the  animal.  He  could  prove  the  toxic  character  of  their 
urine  on  other  animals.  This  combined  with  starvation 
could  sufficiently  account  for  the  short  duration  of 
life.  The  facts  of  the  case  show  that  it  is  due  to  an 
imperfection  in  the  construction  of  the  organism  such 
as  one  would  expect  to  find  more  or  less  in  each  animal 
if  one  discards  the  idea  of  purposefulness  and  divine  wis- 
dom in  nature.  Only  a  slight,  perhaps  an  infinitesimal, 
fraction,  of  those  species  which  are  theoretically  possible 
and  which  at  one  time  or  another  arise  can  survive. 
Those  which  are  durable  show  all  transitions  from 
the  grossest  disharmonies  to  an  apparent  lack  of  such 
shortcomings. 

5.  Minot  had  tried  to  prove  that  the  death  of  meta- 
zoa  is  due  to  the  greater  differentiation  and  special- 
ization of  their  tissues.  Admitting  the  immortality  of 
the  unicellular  organisms  he  argues  that  death  is  the 
price  metazoa  pay  for  the  higher  differentiation  of  their 
cells.  This  is  of  course  purely  metaphorical,  but  we 
may  put  it  into  a  form  in  which  it  is  capable  of  discus- 
sion in  physicochemical  terms,  by  assuming  that  death 
is  a  necessary  stage  in  the  development  of  a  species. 
We  are  incHned,  however,  to  follow  Metchnikoff  and 
suspect  some  poison  accidentally  or  unavoidably  formed 
in  the  body  or  some  structural  shortcoming  as  the  cause 
of  "natural"  death. 


Death  and  Dissolution  of  the  Organism  363 

An  unusually  favourable  object  for  the  study  of 
natural  death  is  the  animal  egg.  The  egg  of  the  starfish 
Asterias  forbesii  when  taken  out  of  the  body  is  usually 
immature,  but  in  the  spawning  season  it  ripens  in  sea 
water.  The  writer^  observed  that  eggs  which  ripen 
disintegrate  very  rapidly  when  not  fertilized.  This 
disintegration  may  be  due  to  a  process  of  autolysis, 
which  sets  in  only  after  the  egg  has  extruded  the  two 
polar  bodies.  The  writer  found  that  by  preventing 
the  maturation  of  the  egg  either  by  withdrawing  the 
oxygen  or  by  replacing  the  alkaline  sea  water  by  a 
neutral  solution  or  by  exposing  the  eggs  for  some  time 
to  acidulated  sea  water,  the  disintegration  could  also 
be  prevented. 

Further  experiments  showed  that  even  in  the  mature 
egg  rapid  disintegration  could  be  prevented  by  lack  of 
oxygen,  and  similar  results  were  obtained  by  Mathews. 
When  the  egg  is  fertilized  it  does  not  disintegrate 
in  the  presence  of  oxygen  but  it  gradually  dies  in 
the  absence  of  oxygen.  One  is  almost  tempted  to 
say  that  while  the  fertilized  egg  is  a  strict  aerobe  the 
mature  unfertilized  egg  is  an  anaerobe.  This  latter 
statement,  however,  becomes  doubtful  since  the  pre- 
sence of  oxygen  may  help  the  disintegration  only  in- 
directly by  allowing  certain  changes  to  go  on  in  the 
egg.  The  important  points  for  us  are  that  duration  of 
life  in  the  mature  unfertilized  egg  is  comparatively 

»  Loeb,  J.,  Biol.  Bull.,  1902,  iii.,  295. 


364  Death  and  Dissolution  of  the  Organism 

short  and  that  the  entrance  of  a  spermatozoon  or  the 
process  of  artificial  parthenogenesis  saves  the  Hfe  of 
the  egg.  Loeb  and  Lewis  found  that  the  Hfe  of  the 
unfertiHzed  sea-urchin  egg  (which  is  usually  mature 
when  removed  from  the  ovaries)  can  also  be  prolonged 
when  its  oxidations  are  suppressed.  The  decay  of  the 
unfertilized  egg  seems  to  be  due  to  the  fact  that  those 
alterations  in  the  cortical  layer  which  underlie  the 
membrane  formation  and  which  are  responsible  for 
the  starting  of  development  gradually  take  place. 
In  such  a  condition  the  egg  will  die  quickly  unless 
deprived  of  oxygen.  This  view  is  supported  by  the 
observation  of  Wasteneys  that  unfertilized  eggs  of 
Arbacia  show  an  increased  rate  of  oxidations  when 
allowed  to  remain  for  some  time  in  sea  water;  we  have 
seen  in  Chapter  V  that  such  an  increase  also  accom- 
panies artificial  membrane  formation. 

6.  If  the  limited  duration  of  life  of  an  organism  is 
determined  by  one  or  more  definite  harmful  chemical 
processes,  we  should  expect  to  find  a  temperature  co- 
efficient for  the  duration  of  life  or  at  least  be  able  to 
show  that  if  all  other  conditions  are  the  same  the  dura- 
tion of  life  is  for  a  given  organism  a  function  of 
temperature.  The  writer'  investigated  the  dura- 
tion of  life  of  fertilized  and  unfertilized  eggs  of 
Strongylocentrotus  purpuratus  for  the  upper  temper- 
ature limits. 

*  Loeb,  J.,  Arch.f.  d.  ges.  Physiol.,  1908,  cxxiv.,  411. 


Death  and  Dissolution  of  the  Organism  365 


TABLE  XX 


Duration  of  life  of  the 

eggs  of  S.  purpuratus 

Temperature 

Unfertilized 

Fertilized 

°C. 

Minutes 

Minutes 

32 

[V/^ 

iK 

31 

{'<r 

30 

l<i 

l<t 

29 

{:? 

28 

j>     8 
(  <  10 

I<:3 

27 

about  18 

j  >  20 
(  <  22 

26 

j  >  35 
1  <40 

j  >35 

(  <40 

25 

(>76 
|<8i 

24 

j  >  168 
1  <  200 

f>  192 

1  <209 

Hours 

22 

joy's 

21 

24 

20 

72 

These  observations  show  a  very  high  temperature 
coefficient  near  the  upper  temperature  limit,  and  this 


366  Death  and  Dissolution  of  the  Organism 

may  account  at  least  partly  for  the  fact  that  in  tropical 
seas  the  pelagic  fauna  is  so  much  more  limited  than  in 
polar  seas.^  It  is  quite  probable  that  the  high  tem- 
perature coefficients  at  the  utmost  limits  are  only  an 
expression  of  the  coagulation  time  of  certain  proteins. 
P.  and  N.  Ran  state  that  in  the  cold  certain  butter- 
flies live  longer,  and  similar  statements  exist  for  the 
silkworm,  but  these  statements  are  not  based  on  exact 
experiments,  which  are  difficult.  Dr.  Northrop  and 
the  writer  have  started  experiments  on  the  influence 
of  temperature  on  the  duration  of  life  of  the  fly  Droso- 
pliila.  Newly  hatched  flies  were  kept  first  without 
food  except  water  and  air  at  34°,  28°,  24°,  19°,  14°, 
and  10°;  and  second  with  cane  sugar.  The  average 
duration  of  life  was  as  follows : 

With  water        days  With  cane  sugar        days 

34'' 2.1 6.2 

28° 2.4 7.2 

24°- • 2.4 9.4 

19° 4-1 12.3 

14° 8.3 

10" II. 9 

'  K.  Brandt  ("Uber  den  Nitratgehalt  des  Ozeanwassers  und  seine 
biologische  Bedeutung,"  Abh.  d.  kais.  Leap.  Carol,  deutsch.  Akad.  d. 
Naturfoscher.,  19 1 5)  accounts  for  this  fact  by  the  assumption  that  through 
the  greater  activity  of  the  denitrifying  bacteria  in  the  tropical  waters 
the  amount  of  available  nitrates  is  here  comparatively  smaller  than 
in  the  polar  oceans.  The  writer  fully  appreciates  the  importance  of  this 
fact  but  nevertheless  is  inclined  also  to  see  a  limiting  factor  in  the 
enormously  rapid  decline  of  the  duration  of  life  at  the  upper  temperature 
limits. 


Death  and  Dissolution  of  the  Organism  367 

These  experiments  show  that  there  is  a  definite 
temperature  coefficient  for  the  duration  of  life  and  that 
this  coefficient  is  of  the  order  of  magnitude  of  that  of 
a  chemical  reaction.  We  are  continuing  these  experi- 
ments with  animals  in  the  presence  of  food.  It  should, 
however,  be  remembered  that  the  fly  carries  with  it 
a  good  deal  of  reserve  material  from  the  larval  period. 
We  have  carried  on  simultaneously  determinations  of 
the  temperature  coefficients  of  the  duration  of  the 
larval  and  pupa  stage  of  these  organisms  at  the  same 
temperatures  and  found  ratios  similar  to  those  given 
above  for  the  duration  of  life  with  water  only. 

7.  Metchnikoff'  has  furnished  the  scientific  facts 
for  our  imderstanding  of  senescence.  He  has  demon- 
strated that  the  changes  in  tissue  which  give  rise  to 
phenomena  of  senihty  are  due  to  the  action  of  phago- 
cytes. Thus  the  ganghon  cells  are  altered  (digested?) 
and  destroyed  by  "  neuronophags "  and  this  is  the 
main  cause  of  mental  seniHty.  Definite  phagocytic 
cells,  the  osteoclasts,  slowly  dissolve  the  bones  (by 
the  excretion  of  an  acid?)  and  this  leads  to  the  known 
fragihty  of  the  bones  in  old  age.  The  whiteness  of 
the  hair  is  due  to  the  action  of  phagocytes;  in  the 
muscles  in  old  age  the  contractile  elements  are  destroyed 
by  the  sarcoplasm,  and  so  on.  It  agrees  with  these 
facts  that  where  organs  are  absorbed  in  the  embryonic 
development  of  an  animal,  as  e.  g.,  the  tail  of  the  tad- 
^  Metchnikoff,  E.,  The  Prolongation  of  Life.     New  York,  1907. 


368  Death  and  Dissolution  of  the  Organism 

pole  in  metamorphosis,  the  phenomenon  is  due  to  a 
process  of  phagocytosis  (and  autolysis).  We  have 
mentioned  the  fact  that  in  the  larva  of  the  Amhly stoma 
the  absorption  of  the  gills  and  of  the  tail  occurs  simul- 
taneously and  that  both  must  be  caused  by  a  constituent 
of  the  blood.  Such  a  constituent  may  be  responsi- 
ble for  phagocytosis  and  autolysis  in  the  organs  under- 
going absorption.  Metchnikoff  calls  attention  to  the 
fact  that  certain  infectious  diseases,  e.  g.,  syphilis,  may 
bring  about  precocious  senility;  and  he  mentions  also 
the  senile  appearance  of  young  cretins  which  is  due  to 
the  diseased  thyroid.  "It  is  no  mere  analogy  to  sup- 
pose that  human  senescence  is  the  result  of  a  slow  but 
chronic  poisoning  of  the  organism."  He  assumes  that 
in  man  this  poisoning  is  caused  by  the'  products  of 
fermentation  in  the  large  intestine  and  that  the  micro- 
organisms responsible  for  these  fermentations  may 
therefore  be  regarded  as  the  real  cause  of  senility  in 
man.  Parrots  which  are  long-lived  birds  have  a  limited 
flora  of  microbes  in  their  intestine,  while  cows  and  horses 
which  are  short-lived  in  comparison  with  man  possess 
an  extraordinary  richness  of  the  intestinal  flora.  But, 
needless  to  say,  it  is  not  the  quantity  of  microbes  alone 
which  is  to  be  considered,  the  nature  of  the  microbes  is 
of  much  greater  importance. 

Certain  plants  like  the  Californian  Sequoia  gigantea 
may  be  considered  as  practically  immortal  since  they 
live  several  thousands  of  years;  other  plants,  the  an- 


Death  and  Dissolution  of  the  Organism  369 

nuals,  die  after  fructification.  Metchnikoff  quotes 
from  a  letter  by  de  Vries  that  this  author  prolonged 
the  life  of  GLnotheras  by  cutting  the  flowers  before 
fertilization. 

Under  ordinary  conditions  the  stem  dies  after  producing 
from  forty  to  fifty  flowers,  but  if  cutting  be  practised  new 
flowers  are  produced  until  the  winter  cold  intervenes.  By 
cutting  the  stem  sufficiently  early  the  plants  are  induced 
to  develop  new  buds  at  the  base  and  these  buds  survive 
winter  and  resume  growth  in  the  following  spring. 

Metchnikoff  suggests  that  it  is  a  poison  formed  in  the 
plant  (in  connection  with  fructification?)  which  kills 
the  annuals,  while  it  is  not  formed  or  is  less  harmful 
in  the  perennials.  He  compares  the  situation  to  the 
death  of  the  lactic  acid  bacilli  if  the  lactic  acid  is  allowed 
to  accumulate.  This  hypothesis  is  certainly  worthy 
of  consideration,  and  it  is  quite  possible  that  in  addi- 
tion to  structural  shortcomings  poisons  formed  by 
certain  organs  of  the  body  as  well  as  poisons  formed 
by  bacteria  account  for  the  phenomenon  of  death  in 
metazoa. 


24 


INDEX 


Abraxas,  203,  238,  241 

Acquired   characters,   inheritance 

of,  337  ff; 
Actinia  equina,  361 
Adaptation,   12,  318  ff.;  to  life  in 

caves,  319   ff.;   fresh   and   salt 

water,  327  ff.;  poisons,  332  ff.; 

temperature,  334  ff.;  caused  by 

hormones,  342 
Addison,  W.  H.  F.,  188 
Agglutination,    of    corpuscles    by 

sera,  67  ff . ;  of  sperm,  78,  82  ff, 
Allolobophora  terrestris,  46 
Alpheus,  176 

Alytes  ohstetricans,  337,  338 
Amanita  phalloides,  63 
Amblystoma,  157,  368 
Amelung,  184 
Amphipyra,  283 
Analogies     between    living    and 

dead  matter,  14  ff. 
Anaphylaxis  reaction,  61  ff. 
Ancel,  158,  225  ff. 
Antagonistic     salt    action.       See 

Balanced  salt  solutions. 
Antennularia  antennina,  194,  196 
Apes,  blood  relationship  to  man, 

54,  56  ff. 
Apolant,  45 
Arbacia,  75  ff.,  96,  99,   loi,   III, 

114,   150,   190  ff.,  293  ff.,  298, 

299,  364 

Arenicola,  277 

Armstrong,  E.  P.,  26,  28,  354 

Arrhenius,  S.,  33  ff.,  88,  290, 296 

Arrhenoidy,  218,  225 

Artificial  parthenogenesis,  95  ff.; 
in  sea  urchins,  95  ff.;  new 
method  of,  98,  99;  by  blood, 
loi  ff.;  by  sperm  extract,  103; 


by  acids,  105;  by  mechanical 
agitation,  107;  in  starfish,  no; 
r61e  of  hypertonic  solution,  112, 
115,  116;  and  oxidation,  116, 
117,  118;  and  permeability, 
119  ff.;  in  frogs,  124;  and  de- 
termination of  sex,  125 

Artificial  production  of  life,  38-39 

Assimilation  of  CO2  without 
chlorophyll,  17  ff. 

Astenas,  ^(),  81,  no,  363;  ochraceaf 
73  ff.;  capilata,  74 

Asterina,  75,  81,  no 

Astrospheres,  115  ff.,  192 

Auer,  J.,  315 

Autolysis,  351  ff. 

Avena,  263 

B.  coli  communis,  ^6;  typhosus,  36; 

fiuorescens,  334 
Bacteria,  growth  of,  15  ff.,  29,  71 

ff.;  specificity  in,  41  ff. 
"  Bacterio-purpurin,"  41 
Balanced  salt  solutions,  307-317; 

theory  of,  317;  and  adaptation, 

331  ff. 
Balanus,  259 
Baltzer,  P.,  215  ff. 
Bancroft,  F.  W.,  70,  125,  127,  264, 

269  ff. 
Bang,  63 

Bardeen,  C.  R.,  174  ff. 
Barnacle,  larvse  of,  313  ff. 
Bataillon,  124 

Bateson,  W.,  230,  240  ff.,  338,  348 
Batrachia,  338 
Baur,  E.,  48,  246 
Bayliss,  63 
Becquerel,  P.,  36  ff. 
Beggiatoa,  19 


371 


3/2 


Index 


Beijerinck,  M.,  20 

Berkeley,  Lord,  III 

Bernard,   Claude,  2  S.,  26,    159, 

350,  354,  355,  358 

Berthelot,  290 

Bertrand;  G.,  248  ff. 

Beutner,  R.,  140 

Bichat,  2,  349 

Bickford,  E.  E.,  169 

Blaauw,  H.  A.,  263 

Blackman,  F.  F.,  302 

Blastomeres,  141  ff. 

Blind  animals,  319  ff. 

Blood,  transfusion  of,  53  ff. 

Blood  relationship,  established  by 
transfusion,  53,  54  ff.;  precipitin 
reaction,  55  ff.;  anaphylaxis  re- 
action, 61  ff.;  hemoglobin  crys- 
tals, 64  ff. 

Blood  serum,  precipitin  reaction 
of,  54  ff.;  effect  of,  on  unfer- 
tilized eggs,  loi  ff.,  124 

Blowfly,  heliotropism  of  larvas  of, 
265  ff. 

Bohn,  G.,  253,  264,  269 

Bombinator  igneus,  46 

Bonellia,  215 

Bonnet,  154,  161 

Bordet,  54  ff.,  60 

Bouin,  158,  225  ff. 

Boveri,  Th.,  8,  126,  128  ff.,  134, 
138  ff.,  150  ff.,  186  ff.,  209  ff., 
246 

Brachystola,  199 

Bradley,  H.  C,  27,  64,  353,  354 

Brandt,  366 

Braus,  H.,  147 

Bridges,  C.  B.,  208,  229,  231  ff. 

Brown,  A.  P.,  64  ff. 

Bruchmann,  H.,  93 

Bryophyllum  calycinum,  153,  160 
ff.,  177 

Buchner,  24 

Budgett,  358 

Buller,  93 

Bunsen-Roscoe,  law  of,  11,  256  ff., 
261,  263,  264 

Burrows,  31 

Campanularia,  178,  181 
Cannon,  V7.  B.,  285 
Carcinus  manas,  21^ 


Cardamine  pratensis,  90 

Carrel,  31 

Cassia  bicapsularis,  37 

Castle,  W.  E.,  89  ff.,  335 

Caullery,  M.,  158,  180,  217 

Cave  animals,  319  ff. 

Cell  division,  15,  29,  129  ff.; 
suppression     of,      113     ff. 

Cells,  nutritive  media  of,  15  ff; 
immortality  of,  30  ff.;  mi- 
grating, 44;  mesenchyme,  51  ff., 
130  ff.,  147,  155  ff. 

Cerianthus  membranaceus,  171  ff., 
188,361 

ChcEtopterus,  78  ff. 

Chamberlain,  M.  M.,  293,  297 

Chapman,  H.  G.,  60 

Chemotropism  of  spermatozoa, 
92  ff. 

Chevreul,  289 

Child,  C.  M.,  7,  170,  177,  358 

Chlamydomonas,  277 

Chodat,  R.,  248 

Chologaster,  320 

Christen,  288 

Chromosomes,  r61e  of,  in  sex 
determination,  198  ff.;  theory  of 
Mendelian  heredity,  233 

Chun,  142 

Ciona  intestinalis,  89  ff.,  212 

Cladocera,  159 

Clausen,  H.,  302 

Clavellina,  181 

Cohen,  E.,  292 

Cohn,  41  ff. 

Compton,  90 

Conklin,    E.    G.,    129,    134,    143, 

145  ff. 
Constancy  of  species,  40-43 
Copernicus,  346 

Corpus  luteum,  action  of,  157-158 
Correlation,  154,  167 
Correns,  C,  90  ff.,  214 
Cramer,  289 

Crampton,  H,  E.,  143,  225 
Criodrilus  lacuum,  219-220 
Crossing    over    of    chromosomes, 

241  ff. 
Crystals,  differences  between  living 

organisms  and,  14  ff. 
Ctenolabrus,  355,  357,  359 
Ctenophores,  Ij^2 


Index 


373 


Cninot,  L.,  12,  324 
Cullen,  G.  E,,  24,  291 

Cuma  rathkii,  318 
CyanophycecB,  287 
Cytisus  biflorus,  37 
Cytoplasm     of    eggs    as     future 
embryo,  8,  9,  70,  126,  151  ff. 


Dakin,  352 

Dallinger,  334 

Daphnia,  210,  262,  279,  280,  282, 

306,  312 
Darbishire,  A.  D.,  347 
Darwin,  90,  297,  346  ff. 
Darwinian  theory,  5  ff. 
Davenport,  C.  B.,  244,  335 
Death,  349  ff.;  natural,  cause  of, 

364,  369  ,    , 

Decidua    formation    mduced    by 

corpus  luteum,  157-158 
Delage,  Y.,  107,  no,  iii,  123,  126, 

186 
de  la  Rive,  24 
de  Meyer,  J.,  127 
Dendrostoma,  loi 
Dentalium,  144 
Design,  4,  5 
Determination  of  sex,  in  bees,  208 

ff.;    in    phylloxerans,    210;    in 

Bonellia,  215 
Development  of  egg,  127  ff. 
de  Vries,  H.,  6,  42,  154,  161,  347, 

369 
Dewitz,  93 

Dieudonn^,  C,  334,  337 
"Directive  force,"  2 
Disharmonies,  7 
Divisibility  of  living  matter,  limits 

of,  148-15 1 
Dominance,  230 
Doncaster,  L.,  203 
Dorfmeister,  303 
Driesch,  H.,  4  ff.,  128,  133,  136, 

138  ff.,  147,  150,  169  ff.,  180  ff., 

184  ff. 
Drosophila   ampelophila,    204    ff., 

237,  243,  322,  347,  366 
Duclaux,  E.,  288,  289 
V.  Dungern,  80 
Duration  of  life,  360  ff. 
Durham,  249 


Dutrochet,  154 
Dzierzon,  208 

Ectoderm  formation,  130  ff. 

Egg,  as  the  future  embryo,  8,  9, 
70,  126,  151;  artificial  partheno- 
genesis of,  95  ff.;  organisms 
from,  128  ff.;  determining  unity 
of  organism,  151-152;  chromo- 
somes in, 1 98  ff. 

Egg  structure,  129  ff.;  influence  of 
centrifugal  force  on,  135;  and 
regulation,  139,  140,  141;  and 
fluidity  of  protoplasm,  141 

Ehrlich,  45,  322,  332  ff.,  341; 
side-chain  theory  of,  88,  188 

Eigenmann,  320,  323  ff. 

Electromotive  forces,  origin  in 
living  organs,  140 

Engelmann,  357 

Engler,  24 

Entelechy,  4,  170,  182 

Environment,  influence  of,  286  ff.; 
temperature,  288  ff.,  344  ff.; 
salinity,  306;  adaptation  to,  319 

Enzyme  action,  23  ff.,  297,  302 

Ernst,  A.,  21 

Eternity  of  life,  34  ff.,  360 

Eudendrium,  260,  261,  269,  277, 
278,326 

Eudorina,  277 

Euglena,  264,  269,  272,  277 

Euler,  H.,  21 

Evolution,  346  ff . ;  and  mutation, 

348 
Ewald,  W.  P.,  261  ff.,  269, 280, 301 

Farmer,  J.  B.,  347 

Fermi,  350,  354 

Fertilization,  heterogeneous,  48  ff., 
51,  73  ff.;  specificity  in,  71  ff.; 
and  oxidation,  117  ff.;  and  per- 
meability, 119  ff. 

"Fertilizin,"  84,  87  ff.,  93 

Fischel,  187 

Fischer,  303  ff. 

Fish,  55 

Fitness  of  environment,  317 

Fitzgerald,  J.  G.,  63 

Flow  of  substances  and  regenera- 
tion in  Bryophyllum,  161  ff. 


374 


Index 


Fluctuating  variations,  6,  297  flf., 

346  flf. 
Folin,  22 
Food,  influence  on  polymorphism 

in  wasps,  222  ff. 
Food  castration,  224;  influence  on 

sexual  cycle  in  rotifers,  224;  on 

metamorphosis  in  tadpoles,  155 
Ford,  63 
Forssmann,  63 
Fredericq,  351 
Free-martin,    cause    of    sterility, 

218-219 
Friedenthal,  H.,  53  fif.,  60 
Frisch,  K.,  278,  279 
Froschel,  P.,  263 
Fuchs,  H.  M.,  90 
Fucus,  123 
Fundulus    heterocUlus,     51,     116, 

147,  300»  301,  302,  307  ff.,  321 

ff.,  328  ff.,  335,  337,  357  ff. 

Galileo,  346 

Galvanotropism,  1 1,  270  ff.,  319 

Gay,  F.  P.,  62  ff. 

Generation,    spontaneous,    14  ff., 

34 

Genes,  4  ff.,  152,  319 

Genus  and  species,  chemical  basis 
of,  40  ff. 

Geppert,  358  _ 

Germination  in  seeds,  35  ff. 

Giard,  180,  216  ff. 

Godlewski,  E.,  48,  75,  78,  120, 
126,  169 

Godlewski,  E.,  Sr.,  18 

Goebel,  K.,  154,  i6i 

Goldfarb,  A.  J.,  326 

Goldschmidt,  R.,  220  ff. 

Goodale,  H.  D.,  218 

Gortner,  R.,  249 

Graber,  V.,  256,  276 

Grafting,  heteroplastic,  in  animals, 
46;  in  plants,  47 

Gravitation,  influence  on  organ 
formation  in  Antennularia,  194 
ff.;  on  the  egg  of  the  frog,  141 

Gray,  J.,  122 

Gregory,  243 

Groom,  T.  T.,  280 

Growth,  termination  of,  184;  in- 
fluence of  cell  size,  187 


Gudematsch,  J.  F.,  155,  255,  342 
Guyer,  124 
Gynandromorphism,  209 

Haeckel,  346 

Half-embryos  and  whole  embryos, 

141,  142 
Hammond,  J.  H.,  Jr.,  269 
Harden,  16 
Hardesty,  358 
Harmonious  character  of  organism, 

5,  6,  318  ff.,  341  ff. 
Harrison,  31 
Hartley,  11 1 
Healing  of  wound,  187 
Hektoen,  66 
Heliotropism,  11  ff.,  257  ff.,  318; 

heredity  of,  250  ff.;  change  of, 

279,   280  ff.;   and    adaptation, 

318 
Helmholtz,  34 
Hemoglobins,     crystallographic 

measurements  of,  64  ff. 
Henderson,  L.,  317 
Henking,  198  ff. 

Herbst,  C,  97,  147,  193,  306,  310 
Heredity,   of   genus   and   species, 

40  ff.,  70,  151,  152;  Mendelian, 

70,  151  flf.,  229  ff.,  348;  of  sex, 

198;  sex-linked,  203  ff.,  238  ff.; 

and  evolution,  348 
Herlant,  M.,  78  ff.,  115  ff. 
Hermaphroditism,  89  ff.,  212  ff., 

216,  219  ff.     5^6  a/50  Inhibition 

and  Regeneration. 
Hertwig,  O.,  97,  123,  292 
Hertwig,  R.,  95,  97 
Hess,  C.,  278 
Heterogeneous     hybrids,     purely 

maternal,  49,  50 
Heterogeneous       transplantation, 

Murphy's  experiments  on,  44  ff. ; 

limitation  of,  46 
Heteromorphosis,  155,  193-196 
Hill,  C.,  25 
Hippiscus,  199 
Holmes,  S.  J.,  269 
Hoppe-Seyler,  351 
Hormones,  145,  155,  181,  219;  and 

Mendelian    heredity,    245    ff., 

348;  and  adaptation,  342.     See 

also  Organ-forming  substances. 


Index 


375 


Huxley,  346 

Hybridization,   heterogeneous,   in 

sea    urchins,    48    ff.,    73    flf.;in 

fishes,  51;  in  plants  (Mendel's), 

230  fif. 
Hydrolytic    enzymes,    action    of, 

24;  reversible  action  of,  24  fl. 
Hypertonic  solution,  99,  11 1  ff. 

Imitation  of  cell  structures  by 
colloids,  39 

Immortality,  of  cancer  cells,  30; 
of  somatic  cells,  30  ff . ;  of  life  in 
general,  34  ff. 

Inheritance,  of  colour-blindness, 
203,  204,  205 ;  of  eye  pigment  in 
Drosophila,  204  ff.;  of  pigm.ents, 
248  ff.;  of  acquired  characters, 

337  ff- 
Inhibition  of  regeneration  in  Bryo- 

phyllum,  162  ff. 
Inhibition  of  sexual  characters  of 

opposite  sex,  in  pheasants,  218; 

lack  of  in  hermaphrodites,  219; 

in  Bonellia,  226 
Instincts,   10  ff.,  253  ff.;  sexual, 

198  ff. 
Intersexualism,  221 
Intestine,  formation  of,  130  ff. 
Isoagglutinins,  66  ff.,  92 
Isolation  of  blastomeres,  136  ff. 

Jacoby,  352 
Janda,  V.,  219  ff. 
Jansky,  67 
Janssens,  242 
Jennings,  H.  S.,  264  ff. 
Jensen,  45 
Joest,  46 

Johannsen,  W.,  42,  333 
Jones,  352 
Jost,  90 

Kammerer,  P.,  325,  337  ff. 

Kanitz,  A.,  290,  292,  296 

Kastle,  J.  H.,  26  ff. 

Kellogg,  V.  L.,  279 

Kelvin,  34 

King,  W.  O.  R.,  50,  247 

Klug,  351 

V.  KnafH,  E.,  106 

Knowlton,  E.  P.,  292 


Kofoid,  C.  A.,  143 
V.  Korosy,  300 
Korschelt,  361 
Krakatau,  21 
Kraus,  54  ff. 
Krogh,  292 
Kryz,  P.,  335 
Kupelwieser,  H.,  75 

Lack  of  oxygen,  influence  on  dis- 
integration of  tissue,  355  ff. 

Ladoff,  S.,  224 

Lamarck,  6 

Laminaria,  165 

Landois,  L.,  53 

Landsteiner,  66 

Lanice,  143  ff. 

Lankester,  E.  R.,  41 

Leathes,  J.  B.,  63 

Leucana  leucocephala,  37 

Levene,  351,  352 

Lewis,  183,  344,  364 

Light,  influence  on  organ  forma- 
tion, in  cave  animals,  319  ff.; 
in  Protetis,  325;  in  Eudendrium, 
326.     See  also  Heliotropism. 

Lillie,  F.  R.,  80,  82  ff.,  87  ff.,  93, 
134,  191,218,292 

Lillie,  R.  S.,  loi,  107,  no,  120  ff. 

Lipase,  synthetic  action  of,  26 

Living  and  dead  matter,  specific 
differences  between,  14  ff. 

Lloyd,  D.  J.,  Ill 

Localization  of  Mendelian  charac- 
ters in  individual  chromosomes, 
243,  244 

Loeb,  Leo,  30  ff.,  45,  157,  170, 
187  ff.,  342 

Loevenhart,  A.  S.,  26  ff. 

Lumhricus  rubellus,  46 

Lychnis  dioica,  217  * 

Lycopodium,  93 

Lygceus,  201 

Lymantria  dispar,  220 

Lymncsus,  142 

Lymphocytes,  role  of,  45  ff. 

Lyon,  E.  P.,  134  ff. 

Macfadyen,  A.,  36 

Maeterlinck,  255 

Magnus,  W.,  60 

Maltase,  synthetic  action  of,  25 


Zl^ 


Index 


Marchal,  P.,  222  ff.,  254 

Margelis,  192 

Mass  of  chromatin  and  of  cyto- 
plasm, 186 

Mast,  269,  277 

Mathews,  A.  P.,  107,  363 

Matthaei,  G.  L.  C,  302 

Maxwell,  S.  S.,  270,  274,  277 

McClendon,  J.  F.,  122,  322 

McClung,  C.  E.,  68,  198  flf.,  237 

Megusar,  340 

Meignon,  217 

Meisenheimer,  225 

Meltzer,  S.  J.,  315 

Membrane  formation,  86  ff.;  arti- 
ficial, 98  ff. 

Mendel,  G.,  23,  229  ff, 

Mendelian  characters,  and  evolu- 
tion, 70,  348;  and  internal  se- 
cretions, 243,  348;  and  enzymes, 
247,  248,  249 

Mendelian,  factors  of  heredity, 
4  ff.,  68,  151  ff.;  mutation,  66; 
dominant,  90;  segregation, 
229  ff.  See  also  Non-Mendelian 
inheritance. 

Mendelian  heredity,  mechanism 
of,  229  ff.;  and  chromosomes, 
233  ff.;  and  hormones,  245  ff., 
348 ;  and  enzymes,  247  ff. 

Menidia,  51,  321,  323 

Merogony,  120,  126,  186 

Merrifield,  303 

Mesenchyme  formation,  130  ff. 

Metamorphosis  of  tadpoles  in- 
duced by  thyroid,  155,  156 

Metchnikoff,  361  ff.,  367  ff. 

Michaelis,  L,,  62,  317 

Micrococcus  prodigiosus,  334 

Micromeres,  132  ff. 

Minot7  362 

Moenkhaus,  W.  J.,  51,  344 

Molisch,  20 

Montgomery,  199,  234 

Moore,  A.  R.,  50,  247  ff.,  280 

Morgan,  T.  H.,  46,  68,  89  ff.,  95, 
116,  126,  134,  141  ff.,  173,  175, 
184,  204  ff.,  229  ff.,  241  ff.,  244, 

347 
Morse,  M.,  156,  353 
Morton,  J.  J.,  44 
Moss,  W.  L.,  67 


MuUer,  H.  J.,  229,  231  ff. 
Murphy,  J.  B.,  44  ff. 
Mutation,  6,  42,  243;  and  evolu- 
tion, 347,  348 
Myers,  55 

Nathanson,  19 

Natural  death,  361  ff. 

Neilson,  no 

Newman,  344 

Newton's  Law,  253 

Nitrifying  bacteria,  16  ff. 

Non-Ivlendelian  inheritance,  genus 
and  species  characters,  70,  151, 
251;  rate  of  segmentation, 
246;  first  development,  247 

Northrop,  366 

Nostocacece,  21 

Nussbaum,  M.,  149 

Nuttall,  G.  H.  F.,  56  ff. 

Ocneria  dispar,  225 

(Enotherus,  369 

Onslow,  H.,  249 

Organ-forming  substances  or 
hormones  in  regeneration,  I54ff.; 
causing  metamorphosis  in  tad- 
poles, 155-157;  decidua  forma- 
tion, 158;  development  of  milk 
glands,   158;  Sachs's  theory  of, 

159 
Organisms  from  eggs,  128  ff. 
Origin  of  life,  14  ff.,  33  ff. 
Osborne,  23 

Osterhout,  W.  J.  V.,  312 
Ostwald,  Wo.,  29,  305,  312 
Oudemans,  225 
Overton,  123 

Paloemon,  193 

Palwmonetas,  193;  geotropism  of, 

270 
Palinurus,  193 
Pandorina,  277 
Parker,  G.  H.,  264,  269 
Parthenogenesis,  artificial,  95  ff.; 

"spontaneous,"  107 
Pasteur,  14  ff.,  24,  33,  38 
Patten,  B.,  264  ff 
Pauli,  W.,  289 
Pavy,  350 
Payne,  F.,  322 


Index 


zn 


Pearl,  R.,  203,  244 

PeniciUium,  289 

Pennaria,  192 

Pepsin,   synthetic  action   of,   28, 

62,  63 
Pfeffer,  92  ff. 
Phagocytosis,  367 
Planaria,  173  ff.,  177 
Planorbis,  142 
Plants,  heteroplastic  grafting  in, 

47  ff.;  regeneration  in,  160  ff. 
Polygordius,  280 
Polymorphism,  222 
Porthesia,  256,  280  ff. 
Preadaptation,  12,  324 
Precipitin  reaction,  54  ff. 
Preformation  of  organism  in  egg, 

128  ff.,  142-145 
Presence  and  absence theory,23off. 
Primula,  243 
Proteins,    specific    reactions     of, 

54  ff . ;  and  species  specificity,  68 ; 

and  evolution,  70,  348 
Protenor,  200  ff.,  208 
Proteus,  325  ff. 
Przibram,  H.,  176 
Pure  lines,  333,  334 
Pycnopodia  spuria,  74 
Pyrrhocoris,  198 

Radiation  pressure,  r61e  in  trans- 
mission of  spores  through  inter- 
stellar space,  34  ff. 

Rana,  esculenta,  46;  palustris,  46; 
virescens,  46 

Rate  of  segmentation,  a  non- 
Mendelian  hereditary  charac- 
ter, 246 

Rau,  366 

Reaction,  tropistic,  11  ff.,  92  ff., 
147,  178,  187,  255  ff.;  precipi- 
tin, 54  ff.;  anaphylaxis,  61  ff. 

Regeneration,  9  ff.,  153  ff.;  in 
plants,  160  ff.;  in  Bryophyllum, 
161-167;  in  animals,  167  ff.; 
in  Tubularia,  167-170;  in 
Cerianthus,  171  ff.;  in  Planar- 
ians,  173-176;  in  Alpheus,  176; 
and  autolysis,  178-181;  of  lens, 
182,  183;  external  influences 
on,  192  ff.;  of  gonads  in  her- 
maphrodites, 219 


Regulation,     139,     140,     141;    in 

regeneration,  see  Regeneration. 
Reichert,  E.  T.,  64  ff. 
Reseda,  90 
Resistance  of  spores,  36 ;  seeds,  36 

ff. 
Reversibility  of  development,  in 

Campanularia,    178  ff.;    in   As- 

cidians,  180;  in  egg,    189  ff.;  in 

Antennularia,  194 
Rhabdonema  nigrovenosum,  213 
Richet,  C,  61 
Richter,  34 
Ringer  solution,  99 
Robertson,  T.  B.,  28  ff.,  62  ff., 

104,  311 
Roentgen  rays,  45 
Roscoe,  see  Bunsen 
Rotifers,  determination  of  sexual 

cycle  by  food,  224 
Roux,  W.,  141  ff. 

Saccharomyces,  36;  cerevisice,  60 

Sacculina,  216  ff. 

Sachs,  88, 

V.  Sachs,  J.,  145,  154  ff.,  159,  161, 

184 
Salamandra  maculosa,  339 
Salkowski,  352 
Salts  required  for  life,  306  ff. 
Sansum,  W.  D.,  64 
Schizophycece,  21 
Schleip,  W.,  213 
Schoenbein,  358 
Schottelius,  334,  337 
Schroeder,  14,  33 
Schultze,  O.,  141 
Schutze,  55 
Schwann,  33 
Schwarzschild,  34 
Secretions,  internal,  145,  155,  157 
Self-digestion,  350  ff. 
Self-sterihty,  89  ff. 
Senescence,  367 
Sequoia,  31,  368 
Setchell,  W.  A.,  165,  287 
Sex,  of  parthenogenetic  frogs,  125; 

of  twins,  211 
Sex  chromosome,  199  ff. 
Sex     determination,      cytological 

basis  of,    198  ff.;  physiological 

basis  of,  214  ff. 


37^ 


Index 


Sexual  characters,  198  ff. 

Shibata,  93 

ShuU,  A.  F.,  214,  224 

Sicyonia,  193 

Side-chain  theory,  88,  188 

Smith,  Geoffrey,  159,  217 

Smith,  Graham,  58 

Spain,  K.  C.,  188 

Spallanzani,  33 

Species,  chemical  basis  of,  40  ff.; 
specificity  of,  41  ff.;  incompati- 
bility  of,    not   closely   related, 

44  ff. 

Species  specificity,  determined  by 
proteins,  63,  68,  348 ;  apparently 
not  by  nucleins,  69 

Specificity,  of  grafted  tissues,  47; 
of  spermatozoa,  48;  of  blood 
sera,  53  ff.;  infertihzation,  71  ff.; 
of  activation  of  sperm  by  eggs, 
80  ff. 

Spelerpes,  320 

Spermatozoa,  fertilization  of  eggs 
by,  72  ff.;  activation  by  eggs 
of,  80  ff.;  agglutination  of,  82 
ff.;  cluster  formation  of,  83; 
chemotropism  of,  92  ff.;  cul- 
tivating of,  126  ff. ;  chromosomes 
of,  198  ff. 

Spirographis,  260 

Spondylomorutn,  277 

Spontaneous  generation,  33, 38 

Spooner,  G.  B.,  134 

Standfuss,  303 

Staphylococcus  pyogenes  aureus,  36 

Steffenhagen,  K.,  55 

Steinach,  E.,  225  ff.,  254,  343 

Stereotropism,  178,  187,283 

Stevens,  Miss,  68,  199 

Stimulus,  196 

Stockard,  322,  340 

Strassburger,  260 

Streaming  as  means  of  egg  differ- 
entiation, 145,  146 

Strongylocenlrotus  franciscanus,  50, 
52,  75,  81  ff.,  103,  247 

Strongylocenlrotus  lividus,  129 

Strongylocenlrotus  purpuratus,  52, 
73  ff.,  81  ff.,  94,  98  ff.,  103,  108, 
109,  III  ff.,  137,  191,  246  ff., 
293  ff.,  364;  larvae  of,  49  ff. 

Sturtevant,  A.  H.,  229  ff. 


Styela,  146 

Sulphur  bacteria,  19  ff. 
Supergenes,  5,  9,  136,  319 
Sutton,  W.  8.,  68,  233  ff. 
Synthesis    of    living    matter,    by 

micro-organisms,     15    ff.;      by 

enzymes,  24  ff. 
Synthetic  action  of  enzymes,  23 

ff.,38 

TcEuia,  212 

Talbot,  262 

Tammann,  291 

Tanaka,  243 

Taylor,  A.  E,,  27,  69  ff. 

Tchistowitch,  54  ff. 

Teleost  fish,  crosses  of,  6  ff.,  345 

Temperature,  effect  on  heliotrop- 
ism,  280;  upper  limit  for  organ- 
isms, 287  ff.;  effect  on  life,  288 
ff . ;  on  butterflies,  303  ff . ;  adapta- 
tion to,  334  ff. 

Temperature  coefficient,  290  ff., 
305;  for  enzyme,  291;  for  de- 
velopment, 292  ff.;  for  oxida- 
tions, 295;  and  fluctuating  var- 
iation, 296  ff.;  for  [heart-beat, 
300  ff . ;  for  duration  of  life,  366 

Thatcher,  Miss,  181 

Thyroid  inducing  metamorphosis 
in  tadpoles,  155,  156 

Tichomiroff,  95 

Tissue  culture  of  spermatozoa,  127 

Tissues,  transplantation  of,  30  ff., 
44  ff.;  cultivation  of,  31  ff.;  spe- 
cificity of,  44  ff. 

Torrey,  H.  B.,  264,  269 

Tower,  348 

Transfusion  of  blood,  53 

Transplantation,  of  tissues,  30  ff., 
44  ff . ;  of  cancers,  45 ;  of  anlagen, 
148;  of  eye  of  salamander,  157; 
of  testes,  226;  of  ovaries,  227 

Traube,  28 

Treub,  21 

Trial  and  error,  268,  270 

Trifolium  arvense,  37 

Tropisms,  11  ff.,  92  ff.,  147,  178, 
187,  253  ff.;  and  instincts,  253; 
theory  of,  257  ff. 

Tropisms,  in  embryonic  develop- 
ment, 147;  of  cave  animals,  324 


Index 


379 


Trypanosomes,  332  ff. 
Trypsin,  synthetic  action  of,  27 
Tuber  brutnale,  60 
Tubularia  crocea,  171 
Tubulanamesembryanihemum,i6j, 

169,  192 
Twins,  origin  of,  136  ff.;  sex  of, 

211 
Tyndall,  33 
Typhlogobius,  320 
Typhlomolge,  320 
Typhlotrilon,  320,  323 
Tyrosinase,  249,  250 
Tyrosine,  249,  250 

V.  Uexkull,  J.,  4  ff.,  128,  139 
Uhlenhuth,  E.,  157,  183,  187 
Uhlenhuth,  P.,  55,  58,  66,  322 
Underhill,  F.  P.,  23 

Vanessa,     prorsa,      303;     levana, 

303 
Vaney,  217 

Van  Slyke,  D.  D.,  22,  24,  291 
van't  Hoff,  24  ff.,  290,  292,  296 
Variation,  6,  297  ff,,  346-348 


Vitzou,  159 
Volvox,  280 

Walcott,  42,  61 

Warburg,  O.,  117  ff. 

Warming,  41 

Wasps,    polymorphism    in,    222- 

224;  sex  determination,  255    ff. 
Wassermann,  55 
Wasteneys,   H.,  29,   82,  87,    112, 

113,    117,    191,   277,   293,   295, 

335,  364 
Weiggert,  188 
Weismann,  7,  30,  303 
Wells,  H.  G.,  62,  69 
Welsh,  D.  A.,  60 
Werner,  F.,  340 
Wheeler,  W.  M.,  43 
White,  J.,  36 
Whitney,  D.  D.,  224 
Wilson,  E.  B.,  68,  143,  199  ff. 
Winkler,  47 

Winogradsky,  S.,  16  ff.,  42 
Wolf,  G.,  182,  187 

Yeast  cells,  cultivation  of,  15  ff. 
Young,  16,  358 


A  Selection  from  the 
Catalogue  of 

G.  P.  PUTNAM'S  SONS 


Complete  Catalogues  sent 
on  application 


Putnam's 
Science    Series 


_^— The  Study  of  Man.      By  Professor  A.  C.  H addon,  M.A.,  D.Sc. 
M.R.I. A.     Fully  illustrated.      8*,  net  $2.00. 
'■'  A  timely  and  useful  volume.     .     .     .     The  author  wields  a  pleasing  pen  and  knows 
how  to  make  the  subject  attractive.     .     .     .     The  work  is  calculated  to  spread  among  its 
readers  an  attraction   to  the   science   of   anthropology.      The  author's  observations  are 
exceedingly  genuine  and  his  descriptions  are  vivid." — London  Athenxum. 

2.— The  Groundwork  of  Science.  A  Study  of  Epistemology.  By 
St.  George  Mivart,  F.R.S.     8*.  net  $i.75- 

"  The  book  is  cleverly  written  and  is  one  of  the  best  works  of  its  kind  ever  put  befon 
the  public.  It  will  be  interesting  to  all  readers,  and  especially  to  those  interested  in  the 
study  of  science." — New  Haven  Leader. 

3. — Rivers  of  North  America.  A  Reading  I.esson  for  Students  of  Geo- 
graphy and  Geology.  By  Israel  C.  Russell,  Professor  of  Geology, 
University  of  Michigan,  author  of  "  Lakes  of  North  America,"  "  Gla- 
ciers of  North  America,"  '•  Volcanoes  of  North  America,"  etc.  Fully 
illustrated.     8°,  net  $2.00. 

"  There  has  not  been  in  the  last  few  years  until  the  present  book  any  authoritative, 
broad  r6sum6  on  the  subject,  modified  and  deepened  as  it  has  been  by  modern  research 
and  reflection,  which  is  couched  in  language  suitable  for  the  multitude.  .  .  .  The  text 
is  as  entertaining  as  it  is  instructive." — Boston  Transcript, 

4.— Earth  Sculpture ;  or,  The  Origin  of  Land-Forms.      By  James 

Geikie,  LL.D.,D.C.L.,  F.R.S.,  etc.,  Murchison  Professor  of  Geology' 

and   Mineralogy  in   the  University   of  Edinburgh  ;   author  of  "  The 

Great  Ice  Age,"  etc.     Fully  illustrated.     8",  net  $2.00. 

"  This  volume  is  the  best  popular  and  yet  scientific  treatment  we  know  of  of  the  ori» 

gin  and  development  of  land-forms,  and  we  immediately  adopted  it  as  the  best  availablo 

text-book  for  a  college  course  in  physiography,    .    .    .    The  book  is  full  of  life  and  vigOTi 

and  shows  the  sympathetic  touch  of  a  man  deeply  iu  love  with  •dMvlz^"— Science. 

5.— Volcanoes :  Their  Structure  and  Significance.  By  T.  G.  Bonney. 
F.R.S.,  University  College,  London.  Fully  illustrated.  8°.  Revised 
and  Enlarged  Edition.     Illustrated.     Net  $2.00. 

"  It  is  not  only  a  fine  piece  of  work  from  a  scientific  point  of  v:"w,  but  It  is  Ulicom. 
monly  attractive  to  the  general  reader,  and  is  likely  to  have  a  larger  sale  than  most  books 
of  its  class." — Springfield  Republican. 

d      Bacteria  :     Especially  as  they  are  related  to  the  economy  of  nature,  to 
industrial  processes,  and  to  the  public  health.      By  George  Newman, 
M.D.,  F.R.S.  (Edin.),  D.P.H.  (Camb.),  etc..  Demonstrator  of  Bac- 
teriology in  King's  College,  London.      With  24  micro-photographs  of 
actual  organisms  and  over  70  other  illustrations.     8°,  net  $2.00. 
''Dr.  Newman's  discussions  of  bacteria  and  disease,  of  immunity,  of  antitoxins,  and 
of  methods  of  disinfection,  are  illuminating,  and  are  to  be  commended  to  all  seeking  la 
formation  on  these  points.     Any  discussion  of  bacteria  will  seem  technical  to  the  uniniti 
ated,  but  all  such  will  find  in  this  book  popular  treatment  and  scientific  accuracy  hapoil^ 
combined." —  The  DiaL 


7.— A  Book  of  Whales.  By  F,  E.  Beddard,  M.A.,  F.R.S.  Illustrated. 
8°.     Net,  $2.00. 

*'  Mr.  Beddard  has  done  well  to  devote  a  whole  volume  to  whales.  They  aie  worthv 
ot  the  biographer  who  has  now  well  grouped  and  described  these  creatures.  The  general 
teader  will  not  find  the  volume  too  technical,  nor  has  the  author  failed  in  bis  attempt  to 
tnoduce  a  book  that  shall  be  acceptable  to  the  zoologist  and  the  naturalist." — N.  V.  Times 

b.  -Comparative  Physiology  of  the  Brain  and  Comparative  Psy- 
chology. With  special  reference  to  the  Invertebrates.  By  Jacques 
LoEB,  M.D.,  Professor  of  Physiology  in  the  University  of  Chicago. 
Illustrated.     8°.     Net,  |i.75- 

_  *'  No  student  of  this  most  interesting  phase  of  the  problems  of  life  can  afford  to  remain 
in  ignorance  of  the  wide  range  of  facts  and  the  suggestive  series  of  interpretations  which 
Professor  Loeb  has  brought  together  in  this  volume." — ^Joseph  Jastrow,  in  the  Chicago 
Dial. 

9. — The  Stars.  By  Professor  Simon  Newcomb,  U.S.N.,  Nautical  Al- 
manac Office,  and  Johns  Hopkins  University.  8°.  Illustrated.  N^ 
$2.00. 

"The  work  is  a  thoroughly  scientific  treatise  on  stars.  The  name  of  the  authoris 
sufficient  guarantee  of  scholarly  and  accurate  watV^— Scientific  American. 

10.— The  Basis  of  Social  Relations.  A  Study  in  Ethnic  Psychology.  By 
Daniel  G.  Brinton,  A.M.,  M.D.,  LL.D.,  Sc.D.,  Late  Professor  of 
American  Archaeology  and  Linguistics  in  the  University  of  Pennsyl- 
vania ;  Author  of  "  History  of  Primitive  Religions,"  "  Races  and 
Peoples,"  "  The  American  Race,"  etc.  Edited  by  Livingston  Far- 
rand,  Columbia  University.     8°.     Net,  $1.50 


Sociology, 

II. — Experiments  on  Animals.  By  Stephen  Paget.  With  an  Intro- 
duction by  Lord  Lister.   Illustrated.    8°.    Net,  $2.00. 

"  To  a  large  class  of  readers  this  presentation  will  be  attractive,  since  it  gives  to  them 
in  a  nut-shell  the  meat  of  a  hundred  scientific  dissertations  in  current  periodical  literature. 
The  volume  has  the  authoritative  sanction  of  Lord  Lister." — Boston  Transcript. 

t2, — Infection  and  Immunity.    With  Special  Reference  to  the  Preventiori 
of  Infectious  Diseases.    By  Geo&ge  M.  Sternberg,  M  D.,  LL.D. 
Surgeon-General  U.  S.  Army  (Retired).    Illustrated.    8°.    Net.  $1.75 

"  A  distinct  public  service  by  an  eminent  authority.  This  admirah'e  litt'e  wor1<  sho'jl 
hf.  a  part  of  the  prescribed  reading  of  the  head  of  every  institution  in  whirl,  children  o. 
vouths  are  gathered.     Conspicuously  useful." — N.  Y.  Times. 

13,— Fatigue,  By  A.  MOSSO,  Professor  of  Physiology  in  the  University 
of  Turin.  Translated  by  Margaret  Drummond,  M.A.,  and  W.  B. 
Drummond.M.B.,  CM.,  F.R.C.P.E.;  extra  Physician,  Royal  Hospital 
for  Sick  Children,  Edinburgh  ;   Author  of  "  The  Child,  His  Nature 

and  Nurture."    Illustrated.     8°.     Net,  $1.50. 

"  A  book  for  the  student  and  for  the  instructor,  full  of  interest,^  also  for  the  intelligent 
general  reader.  The  subject  constitutes  one  of  the  most  fascinating  chapters  in  the  his» 
tory  of  medical  science  and  of  philosophical  research." — Yorkshire  Post. 


14. — Earthquakes.  In  the  Light  of  the  New  Seismology.  By  Clarence 
E.  Button,  Major,  U.  S.  A.     Illustrated.     8°.     Net,  $2.00. 

"  The  book  summarizes  the  results  of  the  men  who  have  accomplished  the  great 
things  in  their  pursuit  of  seismological  knowledge.  It  is  abundantly  illustrated  and  it 
fills  a  place  unique  in  the  literature  of  modern  science." — Chicago  Tribune. 

15, — The  Nature  of  Man.  Studies  in  Optimistic  Philosophy.  By  Elie 
Metchnikoff,  Professor  at  the  Pasteur  Institute.  Translation  and 
introduction  by  P.  Chambers  Mitchell,  M.A.,  D.Sc.  Oxon.  Illus- 
trated.    8°.     Net,  $1.50. 

"  A  book  to  be  set  side  by  side  with  Huxley's  Essays,  whose  spint  ,'t  carries  a  step 
further  on  the  long  road  towards  its  goal." — Mail  and  Express. 

16. — The  Hygiene  of  Nerves  and  Mind  in  Health  and  Disease.    By 

August  Forel,  M.D.,  formerly  Professor  of  Psychiatry  in  the  Uni- 
versity of  Zurich.     Authorized  Translation.     8°.     Net,  $2.00. 

A  comprehensive  and  concise  summary  of  the  results  of  science  in  its  cnosen  field. 
Its  authorship  is  a  guarantee  that  the  statements  made  are  authoritative  as  far  as  the 
statement  of  an  individual  can  be  so  regarded. 

17. — The  Prolongation  of  Life.    Optimistic  Essays.    By  6lie  Metch- 
NiKOFF,   Sub-Director  of  the    Pasteur  Institute.     Author   of   "  The 
Nature  of  Man,"  etc.     8°.     Illustrated.     Net,  $2.50.    Popular  Edition. 
With  an  introduction  by  Prof.  Charles  S.  Minot.     Net,  $1.75. 

In  his  new  work  Professor  Metchnikoff  expounds  at  |:reater  length,  in  the  light  of 
additional  knowledge  gained  in  the  last  few  years,  his  mam  thesis  that  human  life  is  not 
only  unnaturally  short  but  unnaturally  burdened  with  physical  and  mental  disabilities. 
He  analyzes  the  causes  of  these  disharmonies  and  explains  his  reasons  for  hoping  that 
they  may  be  counteracted  by  a  rational  hygiene. 

18. — The  Solar  System.  A  Study  of  Recent  Observations.  By  Prof. 
Charles  Lane  Poor,  Professor  of  Astronomy  in  Columbia  University. 
8°.     Illustrated.     Net,  $2.00. 

The  subject  is  presented  in  untechnical  language  and  without  the  use  of  mathematics. 
Professor  Poor  shows  by  what  steps  the  precise  Knowledge  of  to-day  has  been  reached  and 
explains  the  marvellous  results  of  modern  methods  and  modern  observations. 

19. — Heredity.  By  J.  Arthur  Thomson,  M.A.,  Professor  of  Natural 
History  in  the  University  of  Aberdeen  ;  Author  of  "  The  Science  of 
Life,"  etc.     8°,     Illustrated.      Net,  $3.50. 

The  aim  of  this  work  is  to  expound,  in  a  simple  manner,  the  facts  cf  heredity  and 
Inheritance  as  at  present  known,  the  general  conclusions  which  have  been  securely 
established,  and  ^he  more  important  theories  which  have  been  formulated. 

20. — Climate — Considered  Especially  in  Relation  to  Man.  By  Robert 
DeCourcy  Ward,  Assistant  Professor  of  Climatology  in  Harvard 
University.     8°.     Illustrated.     Net,  $2.00. 

This  volume  is  intended  for  persons  who  have  not  had  special  training  in  the  tech- 
nicalities of  climatology.  Climate  covers  a  wholly  different  field  from  that  included  in 
the  metccrological  text-books.  It  handles  broad  questions  of  climate  in  a  way  which  hai 
not  been  attempted  in  a  single  volume  The  needs  of  the  teacher  and  student  have  been 
kept  constantly  in  mind. 

21. — Age,  Growth,  and  Death.  By  Charles  S.  Minot,  James  Still- 
man  Professor  of  Comparative  Anatomy  in  Harvard  University, 
President  of  the  Boston  Society  of  Natural  History,  and  Author  of 
"Human  Embryology,''  "A  Laboratory  Text-book  of  Embryology," 
etc.     8°,     Illustrated.     $2.50  net. 

This  volume  deals  with  some  of  the  fundamental  problems  of  biplogy,  ,*nd  presenii 
«  series  of  views  (the  results  of  nearly  thirty  years  of  study),  wl"*'*"  th«  author  haf 
correlated  for  the  first  time  in  systematic  form. 


22. — The  Interpretation  of  Nature.    By  C.  Lloyd  Morgan,  LL.D., 

F.R.S.     Crown  8vo.     Net,  $1.25. 

Dr.  Morgan  seeks  to  prove  that  a  Iselief  in  purpose  as  the  causal  reality  of  which 
nature  is  an  expression  is  not  inconsistent  with  a  full  and  whole-hearted  acceptance 
of  the  explanations  of  naturalism. 

23. — Mosquito  Life.  The  Habits  and  Life  Cycles  of  the  Known  Mos- 
quitoes of  the  United  States ;  Methods  for  their  Control ;  and  Keys  for 
Easy  Identification  of  the  Species  in  their  Various  Stages.  An 
account  based  on  the  investigation  of  the  late  James  William  Dupree, 
Surgeon-General  of  Louisiana,  and  upon  the  original  observations 
by  the  Writer.  By  Evelyn  Groesbeeck  Mitchell,  A.B.,  M.S. 
With  64  Illustrations.     8°.     Net,  $2.00. 

This  volume  has  been  designed  to  meet  the  demand  of  the  constantly  increasing 
number  of  students  for  a  work  presenting  in  compact  form  the  essential  facts  so  far 
made  known  by  scientific  investigation  in  regard  to  the  different  phases  of  this,  as  is 
now  conceded,  important  and  highly  interesting  subject.  While  aiming  to  keep 
within  reasonable  bounds,  that  it  may  be  used  for  work  in  the  field  and  in  the  labora- 
tory, no  portion  of  the  work  has  been  slighted,  or  fundamental  information  omitted, 
in  the  endeavor  to  carry  this  plan  into  effect. 

24. — Thinking,  Feeling,  Doing.     An  Introduction  to  Mental  Science. 

By  E.  W.  Scripture,  Ph.D.,  M.D.,  Assistant  Neurologist  Columbia 

University,  formerly  Director  of  the  Psychological  Laboratory  at 

Yale   University.     189   Illustrations.     2d   Edition,    Revised   and 

Enlarged.     8°,     Net,  $1.75. 

_  "The  chapters  on  Time  and  Action,  Reaction  Time,  Thinking  Time,  Rhythmic 

Action,  and  Power  and  Will  are  most  interesting.     This  book  should  be  carefully 

read  by  every  one  who  desires  to  be  familiar  with  the  advances  made  in  the  study  of 

the  mind,  which  advances,  in  the  last  twenty-five  years,  have  been  quite  as  striking 

and  epoch-making  as  the  strides  made  in  the  more  material  lines  of  knowledge." — 

Jour.  Amer.  Med.  Ass'n.,  Feb.  22,  1908. 

25. — The  World's  Gold.  By  L.  de  Launay,  Professor  at  the  Ecole 
Superieure  des  Mines.  Translated  by  Orlando  Cyprian  Williams. 
With  an  Introduction  by  Charles  A.  Conant,  author  of  "History  of 
Modem  Banks  of  Issue, "  etc.     8°.     Net,  I1.75. 

M.  de  Launay  is  a  professor  of  considerable  repute  not  only  in  France,  but  among 
scientists  throughout  the  world.  In  this  work  he  traces  the  various  uses  and  phases 
of  gold;  first  its  geology;  secondly,  its  extraction;  thirdly,  its  economic  value. 

26. — The  Interpretation  of  Radium.  By  Frederick  Soddy,  Lecturer 
in  Physical  Chemistry  in  the  University  of  Glasgow.  Third  Edi- 
tion, rewritten,  with  data  brought  down  to  1912.  8°.  With  33 
Diagrams  and  Illustrations.     $2.00  net. 

As  the  application  of  the  present-day  interpretation  of  Radium  (that  it  is  an 
element  undergoing  spontaneous  disintegration)  is  not  confined  to  the  physical 
sciences,  but  has  a  wide  and  general  bearing  upon  our  whole  outlook  on  Nature,  Mr. 
Soddy  has  presented  the  subject  in  non-technical  language,  so  that  the  ideas  involved 
are  within  reach  of  the  lay  reader.  No  effort  has  been  spared  to  get  to  the  root  of 
the  matter  and  to  secure  accuracy,  so  that  the  book  should  prove  serviceable  to  other 
fields  of  science  and  investigation,  as  well  as  to  the  general  public. 

27. — Criminal  Man.  According  to  the  Classification  of  Cesare  Lom- 
BROSO,  Briefly  Summarized  by  his  Daughter,  Gina  Lombroso- 
Ferrero.  With  36  Illustrations  and  a  Bibliography  of  Lombroso's 
Publications  on  the  Subject.     8°.     Net  $2.00. 

Signora  Guglielmo  Ferrero's  resum6  of  her  father's  work  on  criminal  anthropo- 
logy is  specially  dedicated  to  all  those  v.-hose  ofiace  it  is  to  correct,  reform,  and  punish 
the  criminal,  with  a  view  to  diminishing  the  injury  caused  to  society  by  his  anti-social 
acts;  also  to  superintendents,  teachers,  and  those  engaged  in  rescuing  orphans  and 
children  of  vicious  habits,  as  a  guide  in  checking  the  development  of  evil  germs  and 
eliminating  incorrigible  subjects  whose  example  is  a  source  of  corruption  to  others. 
28.— The  Social  Evil.     With  Special  Reference  to  Conditions  Existing 
in  the  City  of  New  York.     A  Report  Prepared  in  1902  under  the 
Direction  of  the  Committee  of  Fifteen.     Second  Edition,  Revised, 
with  New  Material  Covering  the  Years  1902-1911.     Edited  by 
Edwin  R.  A.  Seligman,  LL.D.,  McVickar  Professor  of  Pohtical 
Economy  in  Columbia  University.     8vo.     $1.75  net. 
A  study  that  is  far  from  being  of  merely  local  interest  and  application.     The 
problem  is  considered  in  all  its  aspects  and,  for  this  purpose,  reference  has  been  made 
to  conditions  prevailing  in  other  commvmities  and  to  the  different  attempts  foreign 
cities  have  made  to  regulate  vice. 


29- — Microbes  and  Toxins.  By  Etienne  Burnet,  of  the  Pasteur 
Institute,  Paris.  With  an  Introduction  by  Elie  Metchnikoff, 
Sub-Director  of  the  Pasteur  Institute,  Paris.  With  about  71 
Illustrations.     $2.00  net. 

A  well-known  English  authority  said  in  recommending  the  volume:  "Incom- 
parably the  best  book  there  is  on  this  tremendously  important  subject.  In  fact,  I  am 
assured  that  nothing  exists  which  gives  anything  like  so  full  a  study  of  microbiology." 
In  the  volume  are  considered  the  general  functions  of  microbes,  the  microbes  of  the 
human  system,  the  form  and  structure  of  microbes,  the  physiology  of  microbes,  the. 

gathogenic   protozoa,   toxins,   tuberculin  and   mallein,   immunity,   applications   of 
acteriology,  vaccines  and  serums,  chemical  remedies,  etc. 

30. — Problems  of  Life  and  Reproduction.  By  Marcus  Hartog, 
D.  Sc,  Professor  of  Zoology  in  University  College,  Cork.  8vo. 
$2.50  net. 

The  author  uses  all  the  legitimate  arms  of  scientific  controversy  in  assailing 
certain  views  that  have  been  widely  pressed  on  the  general  public  with  an  assurance 
that  must  have  given  many  the  impression  that  they  were  protected  by  the  universal 
consensus  of  biologists.  Among  the  subjects  considered  are:  "The  Cellular  Pedi- 
gree and  the  Problem  of  Heredity";  "The  Relation  of  Brood-Formation  to  Ordinary 
Cell-Division";  "The  New  Force,  Mitokinetism";  "Nuclear  Reduction  and  the 
Function  of  Chroism";  "Fertilization";  "The  Transmission  of  Acquired  Characters"; 
"Mechanism  and  Life";  "The  Biological  Writings  of  Samuel  Butler";  "Interpola- 
tion in  Memory";  "The  Teaching  of  Nature  Ctudy." 

31. — Problems  of  the  Sexes.  By  Jean  Finot,  Author  of  "The  Science 
of  Happiness,"  etc.  Translated  under  authority  by  Mary  J. 
Safford.     8vo,     $2.00  net. 

A  masterly  presentation  of  the  attitude  of  the  ages  toward  women  and  an  elo- 
quent plea  for  her  further  enfranchisement  from  imposed  and  unnatural  limitations. 
The  range  of  scholarship  that  has  been  enlisted  in  the  writing  may  well  excite  one's 
wonder,  but  the  tone  of  the  book  is  popular  and  its  appeal  is  not  to  any  small  section 
of  the  reading  public  but  to  all  the  classes  and  degrees  of  an  age  that,  from  present 
indications,  will  go  down  in  history  as  the  century  of  Woman. 

32. — The  Positive  Evolution  of  Religion.  Its  Moral  and  Social  Re- 
action.    By  Frederic  Harrison.     8vo.     $2.00  net. 

The  author  has  undertaken  to  estimate  the  moral  and  social  reaction  of  various 
forms  of  Religion — beginning  with  Nature  Worship,  Polytheism,  Catholicism, 
Protestantism,  and  Deism.  The  volume  may  be  looked  upon  as  the  final  word,  the 
summary  of  the  celebrated  author's  philosophy — a  systematic  study  of  the  entire 
religious  problem. 

33. — The  Science  of  Happiness.  By  Jean  Finot,  Author  of  "Prob- 
lems of  the  Sexes, "  etc.  Translated  from  the  French  by  Mary  J. 
Safford.     8°.     $1.75  net. 

In  this  work,  which  was  crowned  by  the  Academy,  the  author  considers  a 
subject,  the  solution  of  which  offers  more  enticement  to  the  well-wisher  of  the  race 
than  the  gold  of  the  Incas  did  to  the  treasure-seekers  of  Spain,  who  themselves 
doubtless  looked  upon  the  coveted  yellow  metal,  however  mistakenly,  as  a  key  to 
the  happiness  which  all  are  trying  to  find.  "Amid  the  noisy  tumult  of  life,  amid  the 
dissonance  that  divides  man  from  man,"  remarks  M.  Finot,  "the  Science  of  Happiness 
tries  to  discover  the  divine  link  which  binds  humanity  to  happiness  through  the  soul 
and  through  the  union  of  souls."  The  author  considers  the  nature  of  happiness  and 
the  means  of  its  attainment,  as  well  as  many  allied  questions. 

34 — Genetic  Theory  of  Reality.     Being  the  Outcome  of  Genetic  Logic 

as  Issuing  in  the  .Esthetic  Theory  of  Reality  Called  Pancalism. 
By  James  Mark  Baldwin,  Ph.D.,  D.Sc,  LL.D.,  Foreign  Corre- 
spondent of  the  Institute  of  France,  Author  of  "  History  of  Psycho- 
logy," etc.  _    ,  _ 
The  author  here  states  the  general  results  of  the  extended  studies  m  genetic  and 

social  science  and  anthropology  made  by  him  and  others,  and  gives  a  critical  account 

of  the  history  of  the  interpretation  of  nature  and  man,  both  racial  and  philosophical. 
The  book  offers  an  Introduction  to  Philosophy  from   a  new  point  of  view.       It 

contains,  also,  a  valuable  glossary  of   the  terms  employed   in  these  and  similar 

discussions. 

35 — Mosquito  Control  in  Panama  The  Eradication  of  Malaria  and 
Yellow  Fever  in  Cuba  and  Panama.  By  J.  A.  Le  Prince,  C.E.,  A. 
M.,  Chief  Sanitary  Inspector,  Isthmian  Canal  Commission,  1904- 
1914,  and  A.  J.  Orenstein,  M.D.,  Assistant  Chief  Sanitary  Inspec- 
tor, Isthmian  Canal  Commission.  With  an  introduction  by  L.  O. 
Howard,  Ph.D.,  Entomologist  and  Chief,  Bureau  of  Entomology, 
United  States  Department  of  Agriculture.  8°.  95  illustrations. 
$2.50. 
Mr.  Le  Prince's  books  will  be  not  only  of  great  practical  importance  as  a 

guide  to  future  work  of  the  same  character,  especially  in  the  Tropics,  but  also 

of  permanent  historic  value. 


Date  Due 


% 


s 


%<? 


V«»oe/o 


